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Subject[PATCH 2/3] jbd2,tracing,rcu: jbd2_dev_to_name() is not protect by RCU
Date
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@cn.fujitsu.com>
---
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)
);

--
1.7.4.4


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