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Message-ID: <20071217184531.GA13013@linux.vnet.ibm.com>
Date: Mon, 17 Dec 2007 10:45:31 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
Christoph Hellwig <hch@...radead.org>,
Andrew Morton <akpm@...l.org>, Mike Mason <mmlnx@...ibm.com>,
Dipankar Sarma <dipankar@...ibm.com>,
David Smith <dsmith@...hat.com>
Subject: Re: [patch 1/2] Linux Kernel Markers - Support Multiple Probes
On Tue, Dec 04, 2007 at 01:18:46PM -0500, Mathieu Desnoyers wrote:
> RCU style multiple probes support for the Linux Kernel Markers.
> Common case (one probe) is still fast and does not require dynamic allocation
> or a supplementary pointer dereference on the fast path.
>
> - Move preempt disable from the marker site to the callback.
>
> Since we now have an internal callback, move the preempt disable/enable to the
> callback instead of the marker site.
>
> Since the callback change is done asynchronously (passing from a handler that
> supports arguments to a handler that does not setup the arguments is no
> arguments are passed), we can safely update it even if it is outside the preempt
> disable section.
>
> - Move probe arm to probe connection. Now, a connected probe is automatically
> armed.
>
> Remove MARK_MAX_FORMAT_LEN, unused.
>
> This patch modifies the Linux Kernel Markers API : it removes the probe
> "arm/disarm" and changes the probe function prototype : it now expects a
> va_list * instead of a "...".
>
> If we want to have more than one probe connected to a marker at a given
> time (LTTng, or blktrace, ssytemtap) then we need this patch. Without it,
> connecting a second probe handler to a marker will fail.
>
> It allow us, for instance, to do interesting combinations :
>
> Do standard tracing with LTTng and, eventually, to compute statistics
> with SystemTAP, or to have a special trigger on an event that would call
> a systemtap script which would stop flight recorder tracing.
A few additional questions interspersed. Seconding the question
about where the rcu_read_lock() is that rcu_barrier() interacts
with -- current code might work by accident in vanilla kernels,
but would fail in -rt.
Thanx, Paul
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> CC: Christoph Hellwig <hch@...radead.org>
> CC: Andrew Morton <akpm@...l.org>
> CC: Mike Mason <mmlnx@...ibm.com>
> CC: Dipankar Sarma <dipankar@...ibm.com>
> CC: David Smith <dsmith@...hat.com>
> ---
> include/linux/marker.h | 59 ++-
> include/linux/module.h | 2
> kernel/marker.c | 671 +++++++++++++++++++++++++++++-----------
> kernel/module.c | 7
> samples/markers/probe-example.c | 25 -
> 5 files changed, 548 insertions(+), 216 deletions(-)
>
> Index: linux-2.6-lttng/include/linux/marker.h
> ===================================================================
> --- linux-2.6-lttng.orig/include/linux/marker.h 2007-11-28 08:38:52.000000000 -0500
> +++ linux-2.6-lttng/include/linux/marker.h 2007-11-28 08:41:53.000000000 -0500
> @@ -19,16 +19,23 @@ struct marker;
>
> /**
> * marker_probe_func - Type of a marker probe function
> - * @mdata: pointer of type struct marker
> - * @private_data: caller site private data
> + * @probe_private: probe private data
> + * @call_private: call site private data
> * @fmt: format string
> - * @...: variable argument list
> + * @args: variable argument list pointer. Use a pointer to overcome C's
> + * inability to pass this around as a pointer in a portable manner in
> + * the callee otherwise.
> *
> * Type of marker probe functions. They receive the mdata and need to parse the
> * format string to recover the variable argument list.
> */
> -typedef void marker_probe_func(const struct marker *mdata,
> - void *private_data, const char *fmt, ...);
> +typedef void marker_probe_func(void *probe_private, void *call_private,
> + const char *fmt, va_list *args);
> +
> +struct marker_probe_closure {
> + marker_probe_func *func; /* Callback */
> + void *probe_private; /* Private probe data */
> +};
>
> struct marker {
> const char *name; /* Marker name */
> @@ -36,8 +43,11 @@ struct marker {
> * variable argument list.
> */
> char state; /* Marker state. */
> - marker_probe_func *call;/* Probe handler function pointer */
> - void *private; /* Private probe data */
> + char ptype; /* probe type : 0 : single, 1 : multi */
> + void (*call)(const struct marker *mdata, /* Probe wrapper */
> + void *call_private, const char *fmt, ...);
> + struct marker_probe_closure single;
> + struct marker_probe_closure *multi;
> } __attribute__((aligned(8)));
>
> #ifdef CONFIG_MARKERS
> @@ -49,7 +59,7 @@ struct marker {
> * not add unwanted padding between the beginning of the section and the
> * structure. Force alignment to the same alignment as the section start.
> */
> -#define __trace_mark(name, call_data, format, args...) \
> +#define __trace_mark(name, call_private, format, args...) \
> do { \
> static const char __mstrtab_name_##name[] \
> __attribute__((section("__markers_strings"))) \
> @@ -60,24 +70,23 @@ struct marker {
> static struct marker __mark_##name \
> __attribute__((section("__markers"), aligned(8))) = \
> { __mstrtab_name_##name, __mstrtab_format_##name, \
> - 0, __mark_empty_function, NULL }; \
> + 0, 0, marker_probe_cb, \
> + { __mark_empty_function, NULL}, NULL }; \
> __mark_check_format(format, ## args); \
> if (unlikely(__mark_##name.state)) { \
> - preempt_disable(); \
> (*__mark_##name.call) \
> - (&__mark_##name, call_data, \
> + (&__mark_##name, call_private, \
> format, ## args); \
> - preempt_enable(); \
> } \
> } while (0)
>
> extern void marker_update_probe_range(struct marker *begin,
> - struct marker *end, struct module *probe_module, int *refcount);
> + struct marker *end);
> #else /* !CONFIG_MARKERS */
> -#define __trace_mark(name, call_data, format, args...) \
> +#define __trace_mark(name, call_private, format, args...) \
> __mark_check_format(format, ## args)
> static inline void marker_update_probe_range(struct marker *begin,
> - struct marker *end, struct module *probe_module, int *refcount)
> + struct marker *end)
> { }
> #endif /* CONFIG_MARKERS */
>
> @@ -92,8 +101,6 @@ static inline void marker_update_probe_r
> #define trace_mark(name, format, args...) \
> __trace_mark(name, NULL, format, ## args)
>
> -#define MARK_MAX_FORMAT_LEN 1024
> -
> /**
> * MARK_NOARGS - Format string for a marker with no argument.
> */
> @@ -106,24 +113,30 @@ static inline void __printf(1, 2) __mark
>
> extern marker_probe_func __mark_empty_function;
>
> +extern void marker_probe_cb(const struct marker *mdata,
> + void *call_private, const char *fmt, ...);
> +extern void marker_probe_cb_noarg(const struct marker *mdata,
> + void *call_private, const char *fmt, ...);
> +
> /*
> * Connect a probe to a marker.
> * private data pointer must be a valid allocated memory address, or NULL.
> */
> extern int marker_probe_register(const char *name, const char *format,
> - marker_probe_func *probe, void *private);
> + marker_probe_func *probe, void *probe_private);
>
> /*
> * Returns the private data given to marker_probe_register.
> */
> -extern void *marker_probe_unregister(const char *name);
> +extern int marker_probe_unregister(const char *name,
> + marker_probe_func *probe, void *probe_private);
> /*
> * Unregister a marker by providing the registered private data.
> */
> -extern void *marker_probe_unregister_private_data(void *private);
> +extern int marker_probe_unregister_private_data(marker_probe_func *probe,
> + void *probe_private);
>
> -extern int marker_arm(const char *name);
> -extern int marker_disarm(const char *name);
> -extern void *marker_get_private_data(const char *name);
> +extern void *marker_get_private_data(const char *name, marker_probe_func *probe,
> + int num);
>
> #endif
> Index: linux-2.6-lttng/kernel/marker.c
> ===================================================================
> --- linux-2.6-lttng.orig/kernel/marker.c 2007-11-28 08:38:52.000000000 -0500
> +++ linux-2.6-lttng/kernel/marker.c 2007-11-28 08:41:53.000000000 -0500
> @@ -27,35 +27,41 @@
> extern struct marker __start___markers[];
> extern struct marker __stop___markers[];
>
> +/* Set to 1 to enable marker debug output */
> +const int marker_debug;
> +
> /*
> * markers_mutex nests inside module_mutex. Markers mutex protects the builtin
> - * and module markers, the hash table and deferred_sync.
> + * and module markers and the hash table.
> */
> static DEFINE_MUTEX(markers_mutex);
>
> /*
> - * Marker deferred synchronization.
> - * Upon marker probe_unregister, we delay call to synchronize_sched() to
> - * accelerate mass unregistration (only when there is no more reference to a
> - * given module do we call synchronize_sched()). However, we need to make sure
> - * every critical region has ended before we re-arm a marker that has been
> - * unregistered and then registered back with a different probe data.
> - */
> -static int deferred_sync;
> -
> -/*
> * Marker hash table, containing the active markers.
> * Protected by module_mutex.
> */
> #define MARKER_HASH_BITS 6
> #define MARKER_TABLE_SIZE (1 << MARKER_HASH_BITS)
>
> +/*
> + * Note about RCU :
> + * It is used to make sure every handler has finished using its private data
> + * between two consecutive operation (add or remove) on a given marker. It is
> + * also used to delay the free of multiple probes array until a quiescent state
> + * is reached.
> + */
> struct marker_entry {
> struct hlist_node hlist;
> char *format;
> - marker_probe_func *probe;
> - void *private;
> + void (*call)(const struct marker *mdata, /* Probe wrapper */
> + void *call_private, const char *fmt, ...);
> + struct marker_probe_closure single;
> + struct marker_probe_closure *multi;
> int refcount; /* Number of times armed. 0 if disarmed. */
> + struct rcu_head rcu;
> + void *oldptr;
> + char rcu_pending:1;
> + char ptype:1;
> char name[0]; /* Contains name'\0'format'\0' */
> };
>
> @@ -63,7 +69,8 @@ static struct hlist_head marker_table[MA
>
> /**
> * __mark_empty_function - Empty probe callback
> - * @mdata: pointer of type const struct marker
> + * @probe_private: probe private data
> + * @call_private: call site private data
> * @fmt: format string
> * @...: variable argument list
> *
> @@ -72,13 +79,262 @@ static struct hlist_head marker_table[MA
> * though the function pointer change and the marker enabling are two distinct
> * operations that modifies the execution flow of preemptible code.
> */
> -void __mark_empty_function(const struct marker *mdata, void *private,
> - const char *fmt, ...)
> +void __mark_empty_function(void *probe_private, void *call_private,
> + const char *fmt, va_list *args)
> {
> }
> EXPORT_SYMBOL_GPL(__mark_empty_function);
>
> /*
> + * marker_probe_cb Callback that prepares the variable argument list for probes.
> + * @mdata: pointer of type struct marker
> + * @call_private: caller site private data
> + * @fmt: format string
> + * @...: Variable argument list.
> + *
> + * Since we do not use "typical" pointer based RCU in the 1 argument case, we
> + * need to put a full smp_rmb() in this branch. This is why we do not use
> + * rcu_dereference() for the pointer read.
> + */
> +void marker_probe_cb(const struct marker *mdata, void *call_private,
> + const char *fmt, ...)
> +{
> + va_list args;
> + char ptype;
> +
> + preempt_disable();
> + ptype = ACCESS_ONCE(mdata->ptype);
> + if (likely(!ptype)) {
> + marker_probe_func *func;
> + /* Must read the ptype before ptr. They are not data dependant,
> + * so we put an explicit smp_rmb() here. */
> + smp_rmb();
> + func = ACCESS_ONCE(mdata->single.func);
Do you really need ACCESS_ONCE() in this case? You have it pinned
between a couple of memory barriers, so the compiler cannot move it
very far, right? (Though ACCESS_ONCE() is pretty cheap, so if there
is a software-engineering reason for it, not a problem.)
> + /* Must read the ptr before private data. They are not data
> + * dependant, so we put an explicit smp_rmb() here. */
> + smp_rmb();
And there is an explicit memory barrier associated with the assignment
to mdata->ptype()? Not exactly sure how that needs to interact with
the argument list for the caller... But I am not seeing the memory
barriers near the uses of marker_probe_cb() -- also, this symbol is
exported -- are out-of-tree callers going to know to use memory barriers?
I am not seeing this in the __trace_mark() macro in 2/2.
The set_marker() and disable_marker() calls do seem to use smb_wmb()
properly, but do not seem to be exported. So, the idea is that the
set_marker() call initializes the data structure, and marker_probe_cb()
is interacting with set_marker() rather than with its caller?
So this might make sense if marker_probe_register() is the main API...
> + va_start(args, fmt);
> + func(mdata->single.probe_private, call_private, fmt, &args);
> + va_end(args);
> + } else {
> + struct marker_probe_closure *multi;
> + int i;
> + /*
> + * multi points to an array, therefore accessing the array
> + * depends on reading multi. However, even in this case,
> + * we must insure that the pointer is read _before_ the array
> + * data. Same as rcu_dereference, but we need a full smp_rmb()
> + * in the fast path, so put the explicit barrier here.
> + */
> + smp_read_barrier_depends();
I would argue for rcu_dereference() on the assignment to ptype above
in place of this smp_read_barrier_depends(), but don't feel all that
strongly about it.
> + multi = ACCESS_ONCE(mdata->multi);
> + for (i = 0; multi[i].func; i++) {
> + va_start(args, fmt);
> + multi[i].func(multi[i].probe_private, call_private, fmt,
> + &args);
> + va_end(args);
> + }
> + }
> + preempt_enable();
> +}
> +EXPORT_SYMBOL_GPL(marker_probe_cb);
> +
> +/*
> + * marker_probe_cb Callback that does not prepare the variable argument list.
> + * @mdata: pointer of type struct marker
> + * @call_private: caller site private data
> + * @fmt: format string
> + * @...: Variable argument list.
> + *
> + * Should be connected to markers "MARK_NOARGS".
> + */
> +void marker_probe_cb_noarg(const struct marker *mdata,
Same comments for this function as for marker_probe_cb() above.
> + void *call_private, const char *fmt, ...)
> +{
> + va_list args; /* not initialized */
> + char ptype;
> +
> + preempt_disable();
> + ptype = ACCESS_ONCE(mdata->ptype);
> + if (likely(!ptype)) {
> + marker_probe_func *func;
> + /* Must read the ptype before ptr. They are not data dependant,
> + * so we put an explicit smp_rmb() here. */
> + smp_rmb();
> + func = ACCESS_ONCE(mdata->single.func);
> + /* Must read the ptr before private data. They are not data
> + * dependant, so we put an explicit smp_rmb() here. */
> + smp_rmb();
> + func(mdata->single.probe_private, call_private, fmt, &args);
> + } else {
> + struct marker_probe_closure *multi;
> + int i;
> + /*
> + * multi points to an array, therefore accessing the array
> + * depends on reading multi. However, even in this case,
> + * we must insure that the pointer is read _before_ the array
> + * data. Same as rcu_dereference, but we need a full smp_rmb()
> + * in the fast path, so put the explicit barrier here.
> + */
> + smp_read_barrier_depends();
> + multi = ACCESS_ONCE(mdata->multi);
> + for (i = 0; multi[i].func; i++)
> + multi[i].func(multi[i].probe_private, call_private, fmt,
> + &args);
> + }
> + preempt_enable();
> +}
> +EXPORT_SYMBOL_GPL(marker_probe_cb_noarg);
> +
> +static void free_old_closure(struct rcu_head *head)
> +{
> + struct marker_entry *entry = container_of(head,
> + struct marker_entry, rcu);
> + kfree(entry->oldptr);
> + /* Make sure we free the data before setting the pending flag to 0 */
> + smp_wmb();
> + entry->rcu_pending = 0;
What happens if we are delayed at this point? The remove_marker() check
for rcu_pending() would conclude that an rcu_barrier() was not required,
and would thus fail to execute rcu_barrier(). We would still have some
instructions within free_old_closure() left to execute, right?
Or is free_old_closure() guaranteed to be part of the main kernel rather
than part of a module?
> +}
> +
> +static inline void debug_print_probes(struct marker_entry *entry)
> +{
> + int i;
> +
> + if (!marker_debug)
> + return;
> +
> + if (!entry->ptype) {
> + printk(KERN_DEBUG "Single probe : %p %p\n",
> + entry->single.func,
> + entry->single.probe_private);
> + } else {
> + for (i = 0; entry->multi[i].func; i++)
> + printk(KERN_DEBUG "Multi probe %d : %p %p\n", i,
> + entry->multi[i].func,
> + entry->multi[i].probe_private);
> + }
> +}
> +
> +static struct marker_probe_closure *
> +marker_entry_add_probe(struct marker_entry *entry,
> + marker_probe_func *probe, void *probe_private)
> +{
> + int nr_probes = 0;
> + struct marker_probe_closure *old, *new;
> +
> + WARN_ON(!probe);
> +
> + debug_print_probes(entry);
> + old = entry->multi;
> + if (!entry->ptype) {
> + if (entry->single.func == probe &&
> + entry->single.probe_private == probe_private)
> + return ERR_PTR(-EBUSY);
> + if (entry->single.func == __mark_empty_function) {
> + /* 0 -> 1 probes */
> + entry->single.func = probe;
> + entry->single.probe_private = probe_private;
> + entry->refcount = 1;
> + entry->ptype = 0;
> + debug_print_probes(entry);
> + return NULL;
> + } else {
> + /* 1 -> 2 probes */
> + nr_probes = 1;
> + old = NULL;
> + }
> + } else {
> + /* (N -> N+1), (N != 0, 1) probes */
> + for (nr_probes = 0; old[nr_probes].func; nr_probes++)
> + if (old[nr_probes].func == probe
> + && old[nr_probes].probe_private
> + == probe_private)
> + return ERR_PTR(-EBUSY);
> + }
> + /* + 2 : one for new probe, one for NULL func */
> + new = kzalloc((nr_probes + 2) * sizeof(struct marker_probe_closure),
> + GFP_KERNEL);
> + if (new == NULL)
> + return ERR_PTR(-ENOMEM);
> + if (!old)
> + new[0] = entry->single;
> + else
> + memcpy(new, old,
> + nr_probes * sizeof(struct marker_probe_closure));
> + new[nr_probes].func = probe;
> + new[nr_probes].probe_private = probe_private;
> + entry->refcount = nr_probes + 1;
> + entry->multi = new;
> + entry->ptype = 1;
> + debug_print_probes(entry);
> + return old;
> +}
> +
> +static struct marker_probe_closure *
> +marker_entry_remove_probe(struct marker_entry *entry,
> + marker_probe_func *probe, void *probe_private)
> +{
> + int nr_probes = 0, nr_del = 0, i;
> + struct marker_probe_closure *old, *new;
> +
> + old = entry->multi;
> +
> + debug_print_probes(entry);
> + if (!entry->ptype) {
> + /* 0 -> N is an error */
> + WARN_ON(entry->single.func == __mark_empty_function);
> + /* 1 -> 0 probes */
> + WARN_ON(probe && entry->single.func != probe);
> + WARN_ON(entry->single.probe_private != probe_private);
> + entry->single.func = __mark_empty_function;
> + entry->refcount = 0;
> + entry->ptype = 0;
> + debug_print_probes(entry);
> + return NULL;
> + } else {
> + /* (N -> M), (N > 1, M >= 0) probes */
> + for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
> + if ((!probe || old[nr_probes].func == probe)
> + && old[nr_probes].probe_private
> + == probe_private)
> + nr_del++;
> + }
> + }
> +
> + if (nr_probes - nr_del == 0) {
> + /* N -> 0, (N > 1) */
> + entry->single.func = __mark_empty_function;
> + entry->refcount = 0;
> + entry->ptype = 0;
> + } else if (nr_probes - nr_del == 1) {
> + /* N -> 1, (N > 1) */
> + for (i = 0; old[i].func; i++)
> + if ((probe && old[i].func != probe) ||
> + old[i].probe_private != probe_private)
> + entry->single = old[i];
> + entry->refcount = 1;
> + entry->ptype = 0;
> + } else {
> + int j = 0;
> + /* N -> M, (N > 1, M > 1) */
> + /* + 1 for NULL */
> + new = kzalloc((nr_probes - nr_del + 1)
> + * sizeof(struct marker_probe_closure), GFP_KERNEL);
> + if (new == NULL)
> + return ERR_PTR(-ENOMEM);
> + for (i = 0; old[i].func; i++)
> + if ((probe && old[i].func != probe) ||
> + old[i].probe_private != probe_private)
> + new[j++] = old[i];
> + entry->refcount = nr_probes - nr_del;
> + entry->ptype = 1;
> + entry->multi = new;
> + }
> + debug_print_probes(entry);
> + return old;
> +}
> +
> +/*
> * Get marker if the marker is present in the marker hash table.
> * Must be called with markers_mutex held.
> * Returns NULL if not present.
> @@ -102,8 +358,7 @@ static struct marker_entry *get_marker(c
> * Add the marker to the marker hash table. Must be called with markers_mutex
> * held.
> */
> -static int add_marker(const char *name, const char *format,
> - marker_probe_func *probe, void *private)
> +static struct marker_entry *add_marker(const char *name, const char *format)
> {
> struct hlist_head *head;
> struct hlist_node *node;
> @@ -118,9 +373,8 @@ static int add_marker(const char *name,
> hlist_for_each_entry(e, node, head, hlist) {
> if (!strcmp(name, e->name)) {
> printk(KERN_NOTICE
> - "Marker %s busy, probe %p already installed\n",
> - name, e->probe);
> - return -EBUSY; /* Already there */
> + "Marker %s busy\n", name);
> + return ERR_PTR(-EBUSY); /* Already there */
> }
> }
> /*
> @@ -130,34 +384,42 @@ static int add_marker(const char *name,
> e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
> GFP_KERNEL);
> if (!e)
> - return -ENOMEM;
> + return ERR_PTR(-ENOMEM);
> memcpy(&e->name[0], name, name_len);
> if (format) {
> e->format = &e->name[name_len];
> memcpy(e->format, format, format_len);
> + if (strcmp(e->format, MARK_NOARGS) == 0)
> + e->call = marker_probe_cb_noarg;
> + else
> + e->call = marker_probe_cb;
> trace_mark(core_marker_format, "name %s format %s",
> e->name, e->format);
> - } else
> + } else {
> e->format = NULL;
> - e->probe = probe;
> - e->private = private;
> + e->call = marker_probe_cb;
> + }
> + e->single.func = __mark_empty_function;
> + e->single.probe_private = NULL;
> + e->multi = NULL;
> + e->ptype = 0;
> e->refcount = 0;
> + e->rcu_pending = 0;
> hlist_add_head(&e->hlist, head);
> - return 0;
> + return e;
> }
>
> /*
> * Remove the marker from the marker hash table. Must be called with mutex_lock
> * held.
> */
> -static void *remove_marker(const char *name)
> +static int remove_marker(const char *name)
> {
> struct hlist_head *head;
> struct hlist_node *node;
> struct marker_entry *e;
> int found = 0;
> size_t len = strlen(name) + 1;
> - void *private = NULL;
> u32 hash = jhash(name, len-1, 0);
>
> head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
> @@ -167,12 +429,16 @@ static void *remove_marker(const char *n
> break;
> }
> }
> - if (found) {
> - private = e->private;
> - hlist_del(&e->hlist);
> - kfree(e);
> - }
> - return private;
> + if (!found)
> + return -ENOENT;
> + if (e->single.func != __mark_empty_function)
> + return -EBUSY;
> + hlist_del(&e->hlist);
> + /* Make sure the call_rcu has been executed */
> + if (e->rcu_pending)
> + rcu_barrier();
> + kfree(e);
> + return 0;
> }
>
> /*
> @@ -184,6 +450,7 @@ static int marker_set_format(struct mark
> size_t name_len = strlen((*entry)->name) + 1;
> size_t format_len = strlen(format) + 1;
>
> +
> e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
> GFP_KERNEL);
> if (!e)
> @@ -191,11 +458,20 @@ static int marker_set_format(struct mark
> memcpy(&e->name[0], (*entry)->name, name_len);
> e->format = &e->name[name_len];
> memcpy(e->format, format, format_len);
> - e->probe = (*entry)->probe;
> - e->private = (*entry)->private;
> + if (strcmp(e->format, MARK_NOARGS) == 0)
> + e->call = marker_probe_cb_noarg;
> + else
> + e->call = marker_probe_cb;
> + e->single = (*entry)->single;
> + e->multi = (*entry)->multi;
> + e->ptype = (*entry)->ptype;
> e->refcount = (*entry)->refcount;
> + e->rcu_pending = 0;
> hlist_add_before(&e->hlist, &(*entry)->hlist);
> hlist_del(&(*entry)->hlist);
> + /* Make sure the call_rcu has been executed */
> + if ((*entry)->rcu_pending)
> + rcu_barrier();
> kfree(*entry);
> *entry = e;
> trace_mark(core_marker_format, "name %s format %s",
> @@ -206,7 +482,8 @@ static int marker_set_format(struct mark
> /*
> * Sets the probe callback corresponding to one marker.
> */
> -static int set_marker(struct marker_entry **entry, struct marker *elem)
> +static int set_marker(struct marker_entry **entry, struct marker *elem,
> + int active)
> {
> int ret;
> WARN_ON(strcmp((*entry)->name, elem->name) != 0);
> @@ -226,9 +503,43 @@ static int set_marker(struct marker_entr
> if (ret)
> return ret;
> }
> - elem->call = (*entry)->probe;
> - elem->private = (*entry)->private;
> - elem->state = 1;
> +
> + /*
> + * probe_cb setup (statically known) is done here. It is
> + * asynchronous with the rest of execution, therefore we only
> + * pass from a "safe" callback (with argument) to an "unsafe"
> + * callback (does not set arguments).
> + */
> + elem->call = (*entry)->call;
> + /*
> + * Sanity check :
> + * We only update the single probe private data when the ptr is
> + * set to a _non_ single probe! (0 -> 1 and N -> 1, N != 1)
> + */
> + WARN_ON(elem->single.func != __mark_empty_function
> + && elem->single.probe_private
> + != (*entry)->single.probe_private &&
> + !elem->ptype);
> + elem->single.probe_private = (*entry)->single.probe_private;
> + /*
> + * Make sure the private data is valid when we update the
> + * single probe ptr.
> + */
> + smp_wmb();
> + elem->single.func = (*entry)->single.func;
> + /*
> + * We also make sure that the new probe callbacks array is consistent
> + * before setting a pointer to it.
> + */
> + rcu_assign_pointer(elem->multi, (*entry)->multi);
> + /*
> + * Update the function or multi probe array pointer before setting the
> + * ptype.
> + */
> + smp_wmb();
> + elem->ptype = (*entry)->ptype;
> + elem->state = active;
> +
> return 0;
> }
>
> @@ -240,8 +551,12 @@ static int set_marker(struct marker_entr
> */
> static void disable_marker(struct marker *elem)
> {
> + /* leave "call" as is. It is known statically. */
> elem->state = 0;
> - elem->call = __mark_empty_function;
> + elem->single.func = __mark_empty_function;
> + /* Update the function before setting the ptype */
> + smp_wmb();
> + elem->ptype = 0; /* single probe */
> /*
> * Leave the private data and id there, because removal is racy and
> * should be done only after a synchronize_sched(). These are never used
> @@ -253,14 +568,11 @@ static void disable_marker(struct marker
> * marker_update_probe_range - Update a probe range
> * @begin: beginning of the range
> * @end: end of the range
> - * @probe_module: module address of the probe being updated
> - * @refcount: number of references left to the given probe_module (out)
> *
> * Updates the probe callback corresponding to a range of markers.
> */
> void marker_update_probe_range(struct marker *begin,
> - struct marker *end, struct module *probe_module,
> - int *refcount)
> + struct marker *end)
> {
> struct marker *iter;
> struct marker_entry *mark_entry;
> @@ -268,15 +580,12 @@ void marker_update_probe_range(struct ma
> mutex_lock(&markers_mutex);
> for (iter = begin; iter < end; iter++) {
> mark_entry = get_marker(iter->name);
> - if (mark_entry && mark_entry->refcount) {
> - set_marker(&mark_entry, iter);
> + if (mark_entry) {
> + set_marker(&mark_entry, iter,
> + !!mark_entry->refcount);
> /*
> * ignore error, continue
> */
> - if (probe_module)
> - if (probe_module ==
> - __module_text_address((unsigned long)mark_entry->probe))
> - (*refcount)++;
> } else {
> disable_marker(iter);
> }
> @@ -289,20 +598,27 @@ void marker_update_probe_range(struct ma
> * Issues a synchronize_sched() when no reference to the module passed
It looks like the synchronize_sched() was removed -- the above comment
also needs to be updated, right?
> * as parameter is found in the probes so the probe module can be
> * safely unloaded from now on.
> + *
> + * Internal callback only changed before the first probe is connected to it.
> + * Single probe private data can only be changed on 0 -> 1 and 2 -> 1
> + * transitions. All other transitions will leave the old private data valid.
> + * This makes the non-atomicity of the callback/private data updates valid.
> + *
> + * "special case" updates :
> + * 0 -> 1 callback
> + * 1 -> 0 callback
> + * 1 -> 2 callbacks
> + * 2 -> 1 callbacks
> + * Other updates all behave the same, just like the 2 -> 3 or 3 -> 2 updates.
> + * Site effect : marker_set_format may delete the marker entry (creating a
> + * replacement).
> */
> -static void marker_update_probes(struct module *probe_module)
> +static void marker_update_probes(void)
> {
> - int refcount = 0;
> -
> /* Core kernel markers */
> - marker_update_probe_range(__start___markers,
> - __stop___markers, probe_module, &refcount);
> + marker_update_probe_range(__start___markers, __stop___markers);
> /* Markers in modules. */
> - module_update_markers(probe_module, &refcount);
> - if (probe_module && refcount == 0) {
> - synchronize_sched();
> - deferred_sync = 0;
> - }
> + module_update_markers();
> }
>
> /**
> @@ -310,33 +626,49 @@ static void marker_update_probes(struct
> * @name: marker name
> * @format: format string
> * @probe: probe handler
> - * @private: probe private data
> + * @probe_private: probe private data
> *
> * private data must be a valid allocated memory address, or NULL.
> * Returns 0 if ok, error value on error.
> + * The probe address must at least be aligned on the architecture pointer size.
> */
> int marker_probe_register(const char *name, const char *format,
> - marker_probe_func *probe, void *private)
> + marker_probe_func *probe, void *probe_private)
> {
> struct marker_entry *entry;
> int ret = 0;
> + struct marker_probe_closure *old;
>
> mutex_lock(&markers_mutex);
> entry = get_marker(name);
> - if (entry && entry->refcount) {
> - ret = -EBUSY;
> - goto end;
> - }
> - if (deferred_sync) {
> - synchronize_sched();
> - deferred_sync = 0;
> + if (!entry) {
> + entry = add_marker(name, format);
> + if (IS_ERR(entry)) {
> + ret = PTR_ERR(entry);
> + goto end;
> + }
> }
> - ret = add_marker(name, format, probe, private);
> - if (ret)
> + /*
> + * If we detect that a call_rcu is pending for this marker,
> + * make sure it's executed now.
> + */
> + if (entry->rcu_pending)
> + rcu_barrier();
> + old = marker_entry_add_probe(entry, probe, probe_private);
> + if (IS_ERR(old)) {
> + ret = PTR_ERR(old);
> goto end;
> + }
> mutex_unlock(&markers_mutex);
> - marker_update_probes(NULL);
> - return ret;
> + marker_update_probes(); /* may update entry */
> + mutex_lock(&markers_mutex);
> + entry = get_marker(name);
> + WARN_ON(!entry);
> + entry->oldptr = old;
> + entry->rcu_pending = 1;
> + /* write rcu_pending before calling the RCU callback */
> + smp_wmb();
> + call_rcu(&entry->rcu, free_old_closure);
> end:
> mutex_unlock(&markers_mutex);
> return ret;
> @@ -346,171 +678,166 @@ EXPORT_SYMBOL_GPL(marker_probe_register)
> /**
> * marker_probe_unregister - Disconnect a probe from a marker
> * @name: marker name
> + * @probe: probe function pointer
> + * @probe_private: probe private data
> *
> * Returns the private data given to marker_probe_register, or an ERR_PTR().
> + * We do not need to call a synchronize_sched to make sure the probes have
> + * finished running before doing a module unload, because the module unload
> + * itself uses stop_machine(), which insures that every preempt disabled section
> + * have finished.
> */
> -void *marker_probe_unregister(const char *name)
> +int marker_probe_unregister(const char *name,
> + marker_probe_func *probe, void *probe_private)
> {
> - struct module *probe_module;
> struct marker_entry *entry;
> - void *private;
> + struct marker_probe_closure *old;
> + int ret = 0;
>
> mutex_lock(&markers_mutex);
> entry = get_marker(name);
> if (!entry) {
> - private = ERR_PTR(-ENOENT);
> + ret = -ENOENT;
> goto end;
> }
> - entry->refcount = 0;
> - /* In what module is the probe handler ? */
> - probe_module = __module_text_address((unsigned long)entry->probe);
> - private = remove_marker(name);
> - deferred_sync = 1;
> + if (entry->rcu_pending)
> + rcu_barrier();
> + old = marker_entry_remove_probe(entry, probe, probe_private);
> mutex_unlock(&markers_mutex);
> - marker_update_probes(probe_module);
> - return private;
> + marker_update_probes(); /* may update entry */
> + mutex_lock(&markers_mutex);
> + entry = get_marker(name);
> + entry->oldptr = old;
> + entry->rcu_pending = 1;
> + /* write rcu_pending before calling the RCU callback */
> + smp_wmb();
> + call_rcu(&entry->rcu, free_old_closure);
> + remove_marker(name); /* Ignore busy error message */
> end:
> mutex_unlock(&markers_mutex);
> - return private;
> + return ret;
> }
> EXPORT_SYMBOL_GPL(marker_probe_unregister);
>
> -/**
> - * marker_probe_unregister_private_data - Disconnect a probe from a marker
> - * @private: probe private data
> - *
> - * Unregister a marker by providing the registered private data.
> - * Returns the private data given to marker_probe_register, or an ERR_PTR().
> - */
> -void *marker_probe_unregister_private_data(void *private)
> +static struct marker_entry *
> +get_marker_from_private_data(marker_probe_func *probe, void *probe_private)
> {
> - struct module *probe_module;
> - struct hlist_head *head;
> - struct hlist_node *node;
> struct marker_entry *entry;
> - int found = 0;
> unsigned int i;
> + struct hlist_head *head;
> + struct hlist_node *node;
>
> - mutex_lock(&markers_mutex);
> for (i = 0; i < MARKER_TABLE_SIZE; i++) {
> head = &marker_table[i];
> hlist_for_each_entry(entry, node, head, hlist) {
> - if (entry->private == private) {
> - found = 1;
> - goto iter_end;
> + if (!entry->ptype) {
> + if (entry->single.func == probe
> + && entry->single.probe_private
> + == probe_private)
> + return entry;
> + } else {
> + struct marker_probe_closure *closure;
> + closure = entry->multi;
> + for (i = 0; closure[i].func; i++) {
> + if (closure[i].func == probe &&
> + closure[i].probe_private
> + == probe_private)
> + return entry;
> + }
> }
> }
> }
> -iter_end:
> - if (!found) {
> - private = ERR_PTR(-ENOENT);
> - goto end;
> - }
> - entry->refcount = 0;
> - /* In what module is the probe handler ? */
> - probe_module = __module_text_address((unsigned long)entry->probe);
> - private = remove_marker(entry->name);
> - deferred_sync = 1;
> - mutex_unlock(&markers_mutex);
> - marker_update_probes(probe_module);
> - return private;
> -end:
> - mutex_unlock(&markers_mutex);
> - return private;
> + return NULL;
> }
> -EXPORT_SYMBOL_GPL(marker_probe_unregister_private_data);
>
> /**
> - * marker_arm - Arm a marker
> - * @name: marker name
> + * marker_probe_unregister_private_data - Disconnect a probe from a marker
> + * @probe: probe function
> + * @probe_private: probe private data
> *
> - * Activate a marker. It keeps a reference count of the number of
> - * arming/disarming done.
> - * Returns 0 if ok, error value on error.
> + * Unregister a probe by providing the registered private data.
> + * Only removes the first marker found in hash table.
> + * Return 0 on success or error value.
> + * We do not need to call a synchronize_sched to make sure the probes have
> + * finished running before doing a module unload, because the module unload
> + * itself uses stop_machine(), which insures that every preempt disabled section
> + * have finished.
> */
> -int marker_arm(const char *name)
> +int marker_probe_unregister_private_data(marker_probe_func *probe,
> + void *probe_private)
> {
> struct marker_entry *entry;
> int ret = 0;
> + struct marker_probe_closure *old;
>
> mutex_lock(&markers_mutex);
> - entry = get_marker(name);
> + entry = get_marker_from_private_data(probe, probe_private);
> if (!entry) {
> ret = -ENOENT;
> goto end;
> }
> - /*
> - * Only need to update probes when refcount passes from 0 to 1.
> - */
> - if (entry->refcount++)
> - goto end;
> -end:
> + if (entry->rcu_pending)
> + rcu_barrier();
> + old = marker_entry_remove_probe(entry, NULL, probe_private);
> mutex_unlock(&markers_mutex);
> - marker_update_probes(NULL);
> - return ret;
> -}
> -EXPORT_SYMBOL_GPL(marker_arm);
> -
> -/**
> - * marker_disarm - Disarm a marker
> - * @name: marker name
> - *
> - * Disarm a marker. It keeps a reference count of the number of arming/disarming
> - * done.
> - * Returns 0 if ok, error value on error.
> - */
> -int marker_disarm(const char *name)
> -{
> - struct marker_entry *entry;
> - int ret = 0;
> -
> + marker_update_probes(); /* may update entry */
> mutex_lock(&markers_mutex);
> - entry = get_marker(name);
> - if (!entry) {
> - ret = -ENOENT;
> - goto end;
> - }
> - /*
> - * Only permit decrement refcount if higher than 0.
> - * Do probe update only on 1 -> 0 transition.
> - */
> - if (entry->refcount) {
> - if (--entry->refcount)
> - goto end;
> - } else {
> - ret = -EPERM;
> - goto end;
> - }
> + entry = get_marker_from_private_data(probe, probe_private);
> + WARN_ON(!entry);
> + entry->oldptr = old;
> + entry->rcu_pending = 1;
> + /* write rcu_pending before calling the RCU callback */
> + smp_wmb();
> + call_rcu(&entry->rcu, free_old_closure);
> + remove_marker(entry->name); /* Ignore busy error message */
> end:
> mutex_unlock(&markers_mutex);
> - marker_update_probes(NULL);
> return ret;
> }
> -EXPORT_SYMBOL_GPL(marker_disarm);
> +EXPORT_SYMBOL_GPL(marker_probe_unregister_private_data);
>
> /**
> * marker_get_private_data - Get a marker's probe private data
> * @name: marker name
> + * @probe: probe to match
> + * @num: get the nth matching probe's private data
> *
> + * Returns the nth private data pointer (starting from 0) matching, or an
> + * ERR_PTR.
> * Returns the private data pointer, or an ERR_PTR.
> * The private data pointer should _only_ be dereferenced if the caller is the
> * owner of the data, or its content could vanish. This is mostly used to
> * confirm that a caller is the owner of a registered probe.
> */
> -void *marker_get_private_data(const char *name)
> +void *marker_get_private_data(const char *name, marker_probe_func *probe,
> + int num)
> {
> struct hlist_head *head;
> struct hlist_node *node;
> struct marker_entry *e;
> size_t name_len = strlen(name) + 1;
> u32 hash = jhash(name, name_len-1, 0);
> - int found = 0;
> + int i;
>
> head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
> hlist_for_each_entry(e, node, head, hlist) {
> if (!strcmp(name, e->name)) {
> - found = 1;
> - return e->private;
> + if (!e->ptype) {
> + if (num == 0 && e->single.func == probe)
> + return e->single.probe_private;
> + else
> + break;
> + } else {
> + struct marker_probe_closure *closure;
> + int match = 0;
> + closure = e->multi;
> + for (i = 0; closure[i].func; i++) {
> + if (closure[i].func != probe)
> + continue;
> + if (match++ == num)
> + return closure[i].probe_private;
> + }
> + }
> }
> }
> return ERR_PTR(-ENOENT);
> Index: linux-2.6-lttng/kernel/module.c
> ===================================================================
> --- linux-2.6-lttng.orig/kernel/module.c 2007-11-28 08:40:56.000000000 -0500
> +++ linux-2.6-lttng/kernel/module.c 2007-11-28 08:41:53.000000000 -0500
> @@ -1994,7 +1994,7 @@ static struct module *load_module(void _
> #ifdef CONFIG_MARKERS
> if (!mod->taints)
> marker_update_probe_range(mod->markers,
> - mod->markers + mod->num_markers, NULL, NULL);
> + mod->markers + mod->num_markers);
> #endif
> err = module_finalize(hdr, sechdrs, mod);
> if (err < 0)
> @@ -2589,7 +2589,7 @@ EXPORT_SYMBOL(struct_module);
> #endif
>
> #ifdef CONFIG_MARKERS
> -void module_update_markers(struct module *probe_module, int *refcount)
> +void module_update_markers(void)
> {
> struct module *mod;
>
> @@ -2597,8 +2597,7 @@ void module_update_markers(struct module
> list_for_each_entry(mod, &modules, list)
> if (!mod->taints)
> marker_update_probe_range(mod->markers,
> - mod->markers + mod->num_markers,
> - probe_module, refcount);
> + mod->markers + mod->num_markers);
> mutex_unlock(&module_mutex);
> }
> #endif
> Index: linux-2.6-lttng/include/linux/module.h
> ===================================================================
> --- linux-2.6-lttng.orig/include/linux/module.h 2007-11-28 08:38:52.000000000 -0500
> +++ linux-2.6-lttng/include/linux/module.h 2007-11-28 08:41:53.000000000 -0500
> @@ -462,7 +462,7 @@ int unregister_module_notifier(struct no
>
> extern void print_modules(void);
>
> -extern void module_update_markers(struct module *probe_module, int *refcount);
> +extern void module_update_markers(void);
>
> #else /* !CONFIG_MODULES... */
> #define EXPORT_SYMBOL(sym)
> Index: linux-2.6-lttng/samples/markers/probe-example.c
> ===================================================================
> --- linux-2.6-lttng.orig/samples/markers/probe-example.c 2007-11-28 08:38:52.000000000 -0500
> +++ linux-2.6-lttng/samples/markers/probe-example.c 2007-11-28 08:41:53.000000000 -0500
> @@ -20,31 +20,27 @@ struct probe_data {
> marker_probe_func *probe_func;
> };
>
> -void probe_subsystem_event(const struct marker *mdata, void *private,
> - const char *format, ...)
> +void probe_subsystem_event(void *probe_data, void *call_data,
> + const char *format, va_list *args)
> {
> - va_list ap;
> /* Declare args */
> unsigned int value;
> const char *mystr;
>
> /* Assign args */
> - va_start(ap, format);
> - value = va_arg(ap, typeof(value));
> - mystr = va_arg(ap, typeof(mystr));
> + value = va_arg(*args, typeof(value));
> + mystr = va_arg(*args, typeof(mystr));
>
> /* Call printk */
> - printk(KERN_DEBUG "Value %u, string %s\n", value, mystr);
> + printk(KERN_INFO "Value %u, string %s\n", value, mystr);
>
> /* or count, check rights, serialize data in a buffer */
> -
> - va_end(ap);
> }
>
> atomic_t eventb_count = ATOMIC_INIT(0);
>
> -void probe_subsystem_eventb(const struct marker *mdata, void *private,
> - const char *format, ...)
> +void probe_subsystem_eventb(void *probe_data, void *call_data,
> + const char *format, va_list *args)
> {
> /* Increment counter */
> atomic_inc(&eventb_count);
> @@ -72,10 +68,6 @@ static int __init probe_init(void)
> if (result)
> printk(KERN_INFO "Unable to register probe %s\n",
> probe_array[i].name);
> - result = marker_arm(probe_array[i].name);
> - if (result)
> - printk(KERN_INFO "Unable to arm probe %s\n",
> - probe_array[i].name);
> }
> return 0;
> }
> @@ -85,7 +77,8 @@ static void __exit probe_fini(void)
> int i;
>
> for (i = 0; i < ARRAY_SIZE(probe_array); i++)
> - marker_probe_unregister(probe_array[i].name);
> + marker_probe_unregister(probe_array[i].name,
> + probe_array[i].probe_func, &probe_array[i]);
> printk(KERN_INFO "Number of event b : %u\n",
> atomic_read(&eventb_count));
> }
>
> --
> Mathieu Desnoyers
> Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>
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