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Subject[PATCH] kill-the-BKL: fix unsafe j_flush_mutex lock
Date
Impact: fix a deadlock

The j_flush_mutex is acquired safely in journal.c:
if we can't take it, we free the reiserfs per superblock lock
and wait a bit.

But we have a remaining place in kupdate_transactions() where
j_flush_mutex is still acquired traditionnaly. Thus the following
scenario (warned by lockdep) can happen:

A B

mutex_lock(&write_lock) mutex_lock(&write_lock)
mutex_lock(&j_flush_mutex) mutex_lock(&j_flush_mutex) //block
mutex_unlock(&write_lock)
sleep...
mutex_lock(&write_lock) //deadlock

Fix this by using reiserfs_mutex_lock_safe() in kupdate_transactions().

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
fs/reiserfs/journal.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
index 64dcabd..7976d7d 100644
--- a/fs/reiserfs/journal.c
+++ b/fs/reiserfs/journal.c
@@ -1826,7 +1826,7 @@ static int kupdate_transactions(struct super_block *s,
struct reiserfs_journal *journal = SB_JOURNAL(s);
chunk.nr = 0;

- mutex_lock(&journal->j_flush_mutex);
+ reiserfs_mutex_lock_safe(&journal->j_flush_mutex, s);
if (!journal_list_still_alive(s, orig_trans_id)) {
goto done;
}
--
1.6.1


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