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Commit 229309ca authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
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jbd2: Fix forever sleeping process in do_get_write_access() 



In do_get_write_access() we wait on BH_Unshadow bit for buffer to get
from shadow state. The waking code in journal_commit_transaction() has
a bug because it does not issue a memory barrier after the buffer is
moved from the shadow state and before wake_up_bit() is called. Thus a
waitqueue check can happen before the buffer is actually moved from
the shadow state and waiting process may never be woken. Fix the
problem by issuing proper barrier.

Reported-by: default avatarTao Ma <boyu.mt@taobao.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 667eff35

fs/jbd2/commit.c

+7 −2
Original line number Diff line number Diff line
@@ -760,8 +760,13 @@ void jbd2_journal_commit_transaction(journal_t *journal) 
                   required. */

		JBUFFER_TRACE(jh, "file as BJ_Forget");

		jbd2_journal_file_buffer(jh, commit_transaction, BJ_Forget);

		/* Wake up any transactions which were waiting for this

		   IO to complete */

		/*

		 * Wake up any transactions which were waiting for this IO to

		 * complete. The barrier must be here so that changes by

		 * jbd2_journal_file_buffer() take effect before wake_up_bit()

		 * does the waitqueue check.

		 */

		smp_mb();

		wake_up_bit(&bh->b_state, BH_Unshadow);

		JBUFFER_TRACE(jh, "brelse shadowed buffer");

		__brelse(bh);