On Tue, Jan 03, 2012 at 04:32:45PM +0100, Jan Kara wrote: > Thanks for the analysis. Actually, you fix adds unnecessary overhead. > The problem really is the wrong ordering of prepare_to_wait() and t_updates > check. So attached patch should fix the issue as well without introducing > the overhead. Thanks, applied. - Ted > From 1cd5b8178893f3f186ce93eb1f47664a1a3e81fc Mon Sep 17 00:00:00 2001 > From: Jan Kara <jack@xxxxxxx> > Date: Tue, 3 Jan 2012 16:13:29 +0100 > Subject: [PATCH] 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@xxxxxxxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
