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Date: Tue, 30 Oct 2007 22:08:30 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: Andrew Morton <akpm@...ux-foundation.org>,
Dave Hansen <haveblue@...ibm.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Christoph Hellwig <hch@....de>
Subject: Re: fix marker warnings
* Dave Hansen (haveblue@...ibm.com) wrote:
> I'm seeing these in the latest git:
>
> kernel/marker.c: In function `marker_probe_unregister':
> kernel/marker.c:355: warning: `probe_module' might be used uninitialized in this function
> kernel/marker.c: In function `marker_probe_unregister_private_data':
> kernel/marker.c:389: warning: `probe_module' might be used uninitialized in this function
> kernel/marker.c:392: warning: `entry' might be used uninitialized in this function
>
> It's due to gcc not detecting that the need_update condition is actually
> constant, and will never call marker_update_probes() on an uninitialized
> probe_module.
>
> However, that need_update bit is all due to dropping the mutex before
> calling marker_update_probes(). As far as I can tell, every call to
> marker_update_probes() has this lock dropping behavior just before
> calling it. So, let's just hold the locks over the
> marker_update_probes() and document that it needs to have a lock taken
> instead.
>
> This removes code overall. Untested except for a quick compile.
> Consider it just a style suggestion. :)
>
Ok, just ran it and it seems good. It did not appear as trivial during
development because locking was is a different order until recently.
I wonder what gcc version you are using though, because mine does not
warn about anything. I wonder if it is really necessary to "fix" false
gcc warnings like this. Let's take it as a cleanup.
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> marker_probe_unregister_private_data() also has a bit of a goto mess
> that produces similar warnings. I'll look at it next.
>
> ---
>
> linux-2.6.git-dave/kernel/marker.c | 34 +++++++++++-----------------------
> 1 file changed, 11 insertions(+), 23 deletions(-)
>
> diff -puN kernel/marker.c~fix-marker-warnings kernel/marker.c
> --- linux-2.6.git/kernel/marker.c~fix-marker-warnings 2007-10-30 12:54:36.000000000 -0700
> +++ linux-2.6.git-dave/kernel/marker.c 2007-10-30 13:03:39.000000000 -0700
> @@ -288,12 +288,13 @@ void marker_update_probe_range(struct ma
> * Issues a synchronize_sched() when no reference to the module passed
> * as parameter is found in the probes so the probe module can be
> * safely unloaded from now on.
> + *
> + * must hold markers_mutex
> */
> -static void marker_update_probes(struct module *probe_module)
> +static void __marker_update_probes(struct module *probe_module)
> {
> int refcount = 0;
>
> - mutex_lock(&markers_mutex);
> /* Core kernel markers */
> marker_update_probe_range(__start___markers,
> __stop___markers, probe_module, &refcount);
> @@ -303,7 +304,6 @@ static void marker_update_probes(struct
> synchronize_sched();
> deferred_sync = 0;
> }
> - mutex_unlock(&markers_mutex);
> }
>
> /**
> @@ -320,7 +320,7 @@ int marker_probe_register(const char *na
> marker_probe_func *probe, void *private)
> {
> struct marker_entry *entry;
> - int ret = 0, need_update = 0;
> + int ret = 0;
>
> mutex_lock(&markers_mutex);
> entry = get_marker(name);
> @@ -335,11 +335,9 @@ int marker_probe_register(const char *na
> ret = add_marker(name, format, probe, private);
> if (ret)
> goto end;
> - need_update = 1;
> + __marker_update_probes(NULL);
> end:
> mutex_unlock(&markers_mutex);
> - if (need_update)
> - marker_update_probes(NULL);
> return ret;
> }
> EXPORT_SYMBOL_GPL(marker_probe_register);
> @@ -355,7 +353,6 @@ void *marker_probe_unregister(const char
> struct module *probe_module;
> struct marker_entry *entry;
> void *private;
> - int need_update = 0;
>
> mutex_lock(&markers_mutex);
> entry = get_marker(name);
> @@ -368,11 +365,9 @@ void *marker_probe_unregister(const char
> probe_module = __module_text_address((unsigned long)entry->probe);
> private = remove_marker(name);
> deferred_sync = 1;
> - need_update = 1;
> + __marker_update_probes(probe_module);
> end:
> mutex_unlock(&markers_mutex);
> - if (need_update)
> - marker_update_probes(probe_module);
> return private;
> }
> EXPORT_SYMBOL_GPL(marker_probe_unregister);
> @@ -392,7 +387,6 @@ void *marker_probe_unregister_private_da
> struct marker_entry *entry;
> int found = 0;
> unsigned int i;
> - int need_update = 0;
>
> mutex_lock(&markers_mutex);
> for (i = 0; i < MARKER_TABLE_SIZE; i++) {
> @@ -414,11 +408,9 @@ iter_end:
> probe_module = __module_text_address((unsigned long)entry->probe);
> private = remove_marker(entry->name);
> deferred_sync = 1;
> - need_update = 1;
> + __marker_update_probes(probe_module);
> end:
> mutex_unlock(&markers_mutex);
> - if (need_update)
> - marker_update_probes(probe_module);
> return private;
> }
> EXPORT_SYMBOL_GPL(marker_probe_unregister_private_data);
> @@ -434,7 +426,7 @@ EXPORT_SYMBOL_GPL(marker_probe_unregiste
> int marker_arm(const char *name)
> {
> struct marker_entry *entry;
> - int ret = 0, need_update = 0;
> + int ret = 0;
>
> mutex_lock(&markers_mutex);
> entry = get_marker(name);
> @@ -447,11 +439,9 @@ int marker_arm(const char *name)
> */
> if (entry->refcount++)
> goto end;
> - need_update = 1;
> end:
> + __marker_update_probes(NULL);
> mutex_unlock(&markers_mutex);
> - if (need_update)
> - marker_update_probes(NULL);
> return ret;
> }
> EXPORT_SYMBOL_GPL(marker_arm);
> @@ -467,7 +457,7 @@ EXPORT_SYMBOL_GPL(marker_arm);
> int marker_disarm(const char *name)
> {
> struct marker_entry *entry;
> - int ret = 0, need_update = 0;
> + int ret = 0;
>
> mutex_lock(&markers_mutex);
> entry = get_marker(name);
> @@ -486,11 +476,9 @@ int marker_disarm(const char *name)
> ret = -EPERM;
> goto end;
> }
> - need_update = 1;
> end:
> + __marker_update_probes(NULL);
> mutex_unlock(&markers_mutex);
> - if (need_update)
> - marker_update_probes(NULL);
> return ret;
> }
> EXPORT_SYMBOL_GPL(marker_disarm);
> _
>
>
> -- Dave
>
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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