From 9837d8e982b7e87a7207f90618e45d460e196e6a Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 4 Jan 2012 22:03:11 -0500 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 Signed-off-by: Jan Kara Signed-off-by: "Theodore Ts'o" --- fs/jbd2/transaction.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 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); - if (!atomic_read(&transaction->t_updates)) { - spin_unlock(&transaction->t_handle_lock); - break; - } 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; + } spin_unlock(&transaction->t_handle_lock); write_unlock(&journal->j_state_lock); schedule();