jbd2: fix deadlock while checkpoint thread waits commit thread to finish
This issue was found when I tried to put checkpoint work in a separate thread, the deadlock below happened: Thread1 | Thread2 __jbd2_log_wait_for_space | jbd2_log_do_checkpoint (hold j_checkpoint_mutex)| if (jh->b_transaction != NULL) | ... | jbd2_log_start_commit(journal, tid); |jbd2_update_log_tail | will lock j_checkpoint_mutex, | but will be blocked here. | jbd2_log_wait_commit(journal, tid); | wait_event(journal->j_wait_done_commit, | !tid_gt(tid, journal->j_commit_sequence)); | ... |wake_up(j_wait_done_commit) } | then deadlock occurs, Thread1 will never be waken up. To fix this issue, drop j_checkpoint_mutex in jbd2_log_do_checkpoint() when we are going to wait for transaction commit. Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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@ -113,7 +113,7 @@ void __jbd2_log_wait_for_space(journal_t *journal)
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nblocks = jbd2_space_needed(journal);
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while (jbd2_log_space_left(journal) < nblocks) {
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write_unlock(&journal->j_state_lock);
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mutex_lock(&journal->j_checkpoint_mutex);
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mutex_lock_io(&journal->j_checkpoint_mutex);
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/*
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* Test again, another process may have checkpointed while we
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@ -276,9 +276,22 @@ restart:
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"JBD2: %s: Waiting for Godot: block %llu\n",
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journal->j_devname, (unsigned long long) bh->b_blocknr);
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if (batch_count)
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__flush_batch(journal, &batch_count);
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jbd2_log_start_commit(journal, tid);
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/*
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* jbd2_journal_commit_transaction() may want
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* to take the checkpoint_mutex if JBD2_FLUSHED
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* is set, jbd2_update_log_tail() called by
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* jbd2_journal_commit_transaction() may also take
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* checkpoint_mutex. So we need to temporarily
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* drop it.
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*/
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mutex_unlock(&journal->j_checkpoint_mutex);
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jbd2_log_wait_commit(journal, tid);
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goto retry;
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mutex_lock_io(&journal->j_checkpoint_mutex);
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spin_lock(&journal->j_list_lock);
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goto restart;
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}
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if (!buffer_dirty(bh)) {
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if (unlikely(buffer_write_io_error(bh)) && !result)
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@ -2067,7 +2067,7 @@ int jbd2_journal_wipe(journal_t *journal, int write)
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err = jbd2_journal_skip_recovery(journal);
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if (write) {
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/* Lock to make assertions happy... */
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mutex_lock(&journal->j_checkpoint_mutex);
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mutex_lock_io(&journal->j_checkpoint_mutex);
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jbd2_mark_journal_empty(journal, REQ_SYNC | REQ_FUA);
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mutex_unlock(&journal->j_checkpoint_mutex);
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}
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