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authorJan Kara <jack@suse.cz>2012-01-04 22:03:11 -0500
committerTheodore Ts'o <tytso@mit.edu>2012-01-04 22:03:11 -0500
commit9837d8e982b7e87a7207f90618e45d460e196e6a (patch)
tree639e335810e90680ce0078b36803835d148144b4
parent9b90e5e02896406a6da28a376568003d14c06770 (diff)
jbd2: fix hung processes in jbd2_journal_lock_updates()
Toshiyuki Okajima found out that when running for ((i=0; i < 100000; i++)); do if ((i%2 == 0)); then chattr +j /mnt/file else chattr -j /mnt/file fi echo "0" >> /mnt/file done process sometimes hangs indefinitely in jbd2_journal_lock_updates(). Toshiyuki identified that the following race happens: jbd2_journal_lock_updates() |jbd2_journal_stop() ---------------------------------------+--------------------------------------- write_lock(&journal->j_state_lock) | . ++journal->j_barrier_count | . spin_lock(&tran->t_handle_lock) | . atomic_read(&tran->t_updates) //not 0 | | atomic_dec_and_test(&tran->t_updates) | // t_updates = 0 | wake_up(&journal->j_wait_updates) prepare_to_wait() | // no process is woken up. spin_unlock(&tran->t_handle_lock) | write_unlock(&journal->j_state_lock) | schedule() // never return | We fix the problem by first calling prepare_to_wait() and only after that checking t_updates in jbd2_journal_lock_updates(). Reported-and-analyzed-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com> Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
-rw-r--r--fs/jbd2/transaction.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index a0e41a4c080e..35ae096bed5d 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -517,12 +517,13 @@ void jbd2_journal_lock_updates(journal_t *journal)
break;
spin_lock(&transaction->t_handle_lock);
+ prepare_to_wait(&journal->j_wait_updates, &wait,
+ TASK_UNINTERRUPTIBLE);
if (!atomic_read(&transaction->t_updates)) {
spin_unlock(&transaction->t_handle_lock);
+ finish_wait(&journal->j_wait_updates, &wait);
break;
}
- prepare_to_wait(&journal->j_wait_updates, &wait,
- TASK_UNINTERRUPTIBLE);
spin_unlock(&transaction->t_handle_lock);
write_unlock(&journal->j_state_lock);
schedule();