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Date: Fri, 8 Jul 2011 09:02:32 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] jbd2,tracing,rcu: jbd2_dev_to_name() is not
protect by RCU
On Thu, Jul 07, 2011 at 10:06:24PM -0400, Steven Rostedt wrote:
> On Thu, 2011-06-16 at 09:47 +0800, Lai Jiangshan wrote:
> > TP_printk() is not inside the RCU critical section, so the return value
> > of jbd2_dev_to_name() may be invalid. This fix pass a devname argument to
> > store the result name to void this problem.
> >
> > And ftrace_print_bdevname() is introduced to wrap
> > trace_seq_reserve() and jbd2_dev_to_name().
> >
> > Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>
> Acked-by: Steven Rostedt <rostedt@...dmis.org>
>
> Ted,
>
> Are you going to take these patches? Probably too late for 3.0, but
> maybe can get them into 3.1?
Me too.
Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> -- Steve
>
> > ---
> > fs/jbd2/journal.c | 27 ++++++++++++---------------
> > include/linux/ftrace_event.h | 10 ++++++++++
> > include/linux/jbd2.h | 6 +++---
> > include/trace/events/jbd2.h | 15 ++++++++-------
> > 4 files changed, 33 insertions(+), 25 deletions(-)
> >
> > diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> > index 1c45b6a..c37597a 100644
> > --- a/fs/jbd2/journal.c
> > +++ b/fs/jbd2/journal.c
> > @@ -2427,11 +2427,8 @@ static void __exit journal_exit(void)
> > * jbd2_dev_to_name is a utility function used by the jbd2 and ext4
> > * tracing infrastructure to map a dev_t to a device name.
> > *
> > - * The caller should use rcu_read_lock() in order to make sure the
> > - * device name stays valid until its done with it. We use
> > - * rcu_read_lock() as well to make sure we're safe in case the caller
> > - * gets sloppy, and because rcu_read_lock() is cheap and can be safely
> > - * nested.
> > + * We use caches to cache the results and use rcu_read_lock()
> > + * to protect the caches.
> > */
> > struct devname_cache {
> > struct rcu_head rcu;
> > @@ -2442,34 +2439,35 @@ struct devname_cache {
> > static struct devname_cache __rcu *devcache[1 << CACHE_SIZE_BITS];
> > static DEFINE_SPINLOCK(devname_cache_lock);
> >
> > -const char *jbd2_dev_to_name(dev_t device)
> > +void jbd2_dev_to_name(dev_t device, char *devname)
> > {
> > int i = hash_32(device, CACHE_SIZE_BITS);
> > - char *ret;
> > struct block_device *bd;
> > static struct devname_cache *cache;
> >
> > rcu_read_lock();
> > cache = rcu_dereference(devcache[i]);
> > if (cache && cache->device == device) {
> > - ret = cache->devname;
> > + memcpy(devname, cache->devname, BDEVNAME_SIZE);
> > rcu_read_unlock();
> > - return ret;
> > + return;
> > }
> > rcu_read_unlock();
> >
> > cache = kmalloc(sizeof(struct devname_cache), GFP_KERNEL);
> > - if (!cache)
> > - return "NODEV-ALLOCFAILURE"; /* Something non-NULL */
> > + if (!cache) {
> > + __bdevname(device, devname);
> > + return;
> > + }
> > bd = bdget(device);
> > spin_lock(&devname_cache_lock);
> > if (devcache[i]) {
> > if (devcache[i]->device == device) {
> > kfree(cache);
> > bdput(bd);
> > - ret = devcache[i]->devname;
> > + memcpy(devname, devcache[i]->devname, BDEVNAME_SIZE);
> > spin_unlock(&devname_cache_lock);
> > - return ret;
> > + return;
> > }
> > kfree_rcu(devcache[i], rcu);
> > }
> > @@ -2480,9 +2478,8 @@ const char *jbd2_dev_to_name(dev_t device)
> > } else
> > __bdevname(device, cache->devname);
> > rcu_assign_pointer(devcache[i], cache);
> > - ret = cache->devname;
> > + memcpy(devname, cache->devname, BDEVNAME_SIZE);
> > spin_unlock(&devname_cache_lock);
> > - return ret;
> > }
> > EXPORT_SYMBOL(jbd2_dev_to_name);
> >
> > diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> > index 59d3ef1..2959ead 100644
> > --- a/include/linux/ftrace_event.h
> > +++ b/include/linux/ftrace_event.h
> > @@ -6,6 +6,7 @@
> > #include <linux/percpu.h>
> > #include <linux/hardirq.h>
> > #include <linux/perf_event.h>
> > +#include <linux/jbd2.h>
> >
> > struct trace_array;
> > struct tracer;
> > @@ -28,6 +29,15 @@ const char *ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
> > const char *ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val,
> > const struct trace_print_flags *symbol_array);
> >
> > +static inline const char *ftrace_print_bdevname(struct trace_seq *p, dev_t device)
> > +{
> > + char *bdevname = trace_seq_reserve(p, BDEVNAME_SIZE);
> > +
> > + jbd2_dev_to_name(device, bdevname);
> > +
> > + return bdevname;
> > +}
> > +
> > #if BITS_PER_LONG == 32
> > const char *ftrace_print_symbols_seq_u64(struct trace_seq *p,
> > unsigned long long val,
> > diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> > index 4ecb7b1..964f375 100644
> > --- a/include/linux/jbd2.h
> > +++ b/include/linux/jbd2.h
> > @@ -1331,11 +1331,11 @@ extern int jbd_blocks_per_page(struct inode *inode);
> > #define BUFFER_TRACE2(bh, bh2, info) do {} while (0)
> > #define JBUFFER_TRACE(jh, info) do {} while (0)
> >
> > -/*
> > - * jbd2_dev_to_name is a utility function used by the jbd2 and ext4
> > +/*
> > + * jbd2_dev_to_name is a utility function used by the jbd2 and ext4
> > * tracing infrastructure to map a dev_t to a device name.
> > */
> > -extern const char *jbd2_dev_to_name(dev_t device);
> > +extern void jbd2_dev_to_name(dev_t device, char *bdevname);
> >
> > #endif /* __KERNEL__ */
> >
> > diff --git a/include/trace/events/jbd2.h b/include/trace/events/jbd2.h
> > index bf16545..a9c8b44 100644
> > --- a/include/trace/events/jbd2.h
> > +++ b/include/trace/events/jbd2.h
> > @@ -27,7 +27,7 @@ TRACE_EVENT(jbd2_checkpoint,
> > ),
> >
> > TP_printk("dev %s result %d",
> > - jbd2_dev_to_name(__entry->dev), __entry->result)
> > + ftrace_print_bdevname(p, __entry->dev), __entry->result)
> > );
> >
> > DECLARE_EVENT_CLASS(jbd2_commit,
> > @@ -49,7 +49,7 @@ DECLARE_EVENT_CLASS(jbd2_commit,
> > ),
> >
> > TP_printk("dev %s transaction %d sync %d",
> > - jbd2_dev_to_name(__entry->dev), __entry->transaction,
> > + ftrace_print_bdevname(p, __entry->dev), __entry->transaction,
> > __entry->sync_commit)
> > );
> >
> > @@ -101,7 +101,7 @@ TRACE_EVENT(jbd2_end_commit,
> > ),
> >
> > TP_printk("dev %s transaction %d sync %d head %d",
> > - jbd2_dev_to_name(__entry->dev), __entry->transaction,
> > + ftrace_print_bdevname(p, __entry->dev), __entry->transaction,
> > __entry->sync_commit, __entry->head)
> > );
> >
> > @@ -121,7 +121,8 @@ TRACE_EVENT(jbd2_submit_inode_data,
> > ),
> >
> > TP_printk("dev %s ino %lu",
> > - jbd2_dev_to_name(__entry->dev), (unsigned long) __entry->ino)
> > + ftrace_print_bdevname(p, __entry->dev),
> > + (unsigned long) __entry->ino)
> > );
> >
> > TRACE_EVENT(jbd2_run_stats,
> > @@ -158,7 +159,7 @@ TRACE_EVENT(jbd2_run_stats,
> >
> > TP_printk("dev %s tid %lu wait %u running %u locked %u flushing %u "
> > "logging %u handle_count %u blocks %u blocks_logged %u",
> > - jbd2_dev_to_name(__entry->dev), __entry->tid,
> > + ftrace_print_bdevname(p, __entry->dev), __entry->tid,
> > jiffies_to_msecs(__entry->wait),
> > jiffies_to_msecs(__entry->running),
> > jiffies_to_msecs(__entry->locked),
> > @@ -194,7 +195,7 @@ TRACE_EVENT(jbd2_checkpoint_stats,
> >
> > TP_printk("dev %s tid %lu chp_time %u forced_to_close %u "
> > "written %u dropped %u",
> > - jbd2_dev_to_name(__entry->dev), __entry->tid,
> > + ftrace_print_bdevname(p, __entry->dev), __entry->tid,
> > jiffies_to_msecs(__entry->chp_time),
> > __entry->forced_to_close, __entry->written, __entry->dropped)
> > );
> > @@ -223,7 +224,7 @@ TRACE_EVENT(jbd2_cleanup_journal_tail,
> > ),
> >
> > TP_printk("dev %s from %u to %u offset %lu freed %lu",
> > - jbd2_dev_to_name(__entry->dev), __entry->tail_sequence,
> > + ftrace_print_bdevname(p, __entry->dev), __entry->tail_sequence,
> > __entry->first_tid, __entry->block_nr, __entry->freed)
> > );
> >
>
>
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