Commit e2555fde authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o

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: default avatarEUNBONG SONG <eunb.song@samsung.com>
Reported-by: default avatarTony Luck <tony.luck@gmail.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent a549984b
...@@ -30,15 +30,19 @@ struct journal_head { ...@@ -30,15 +30,19 @@ struct journal_head {
/* /*
* Journalling list for this buffer [jbd_lock_bh_state()] * 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 * This flag signals the buffer has been modified by
* the currently running transaction * the currently running transaction
* [jbd_lock_bh_state()] * [jbd_lock_bh_state()]
*/ */
unsigned b_modified:1; unsigned b_modified;
/* /*
* Copy of the buffer data frozen for writing to the log. * Copy of the buffer data frozen for writing to the log.
......
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