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jbd,jbd2: fix oops in jbd2_journal_put_journal_head()

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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 <eunb.song@samsung.com>
Reported-by: Tony Luck <tony.luck@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Jan Kara 2013-05-13 09:45:01 -04:00 committed by Theodore Ts'o
parent a549984b8c
commit e2555fde41
1 changed files with 6 additions and 2 deletions
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8
include/linux/journal-head.h
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@ -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.