From e2555fde4159467fb579e6ae3c0a8fc33015d0f5 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Mon, 13 May 2013 09:45:01 -0400 Subject: [PATCH] jbd,jbd2: fix oops in jbd2_journal_put_journal_head() Commit ae4647fb (jbd2: reduce journal_head size) introduced a regression where we occasionally hit panic in jbd2_journal_put_journal_head() because of wrong b_jcount. The bug is caused by gcc making 64-bit access to 32-bit bitfield and thus clobbering b_jcount. At least for now, those 8 bytes saved in struct journal_head are not worth the trouble with gcc bitfield handling so revert that part of the patch. Reported-by: EUNBONG SONG Reported-by: Tony Luck Signed-off-by: Jan Kara Signed-off-by: "Theodore Ts'o" --- include/linux/journal-head.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/include/linux/journal-head.h b/include/linux/journal-head.h index 13a3da25ff07..98cd41bb39c8 100644 --- a/include/linux/journal-head.h +++ b/include/linux/journal-head.h @@ -30,15 +30,19 @@ struct journal_head { /* * Journalling list for this buffer [jbd_lock_bh_state()] + * NOTE: We *cannot* combine this with b_modified into a bitfield + * as gcc would then (which the C standard allows but which is + * very unuseful) make 64-bit accesses to the bitfield and clobber + * b_jcount if its update races with bitfield modification. */ - unsigned b_jlist:4; + unsigned b_jlist; /* * This flag signals the buffer has been modified by * the currently running transaction * [jbd_lock_bh_state()] */ - unsigned b_modified:1; + unsigned b_modified; /* * Copy of the buffer data frozen for writing to the log. -- 2.25.1