Re: [PATCH 2/3] jbd2,tracing,rcu: jbd2_dev_to_name() is notprotect by RCU

[Steven Rostedt]

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@xxxxxxxxxxxxxx>

Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

Ted,

Are you going to take these patches? Probably too late for 3.0, but
maybe can get them into 3.1?

-- 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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