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

include/linux/journal-head.h

+6 −2
Original line number Diff line number Diff line
@@ -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.