At 20:25 09/06/09, Chris Mason wrote:
>On Tue, Jun 09, 2009 at 10:46:55AM +0900, Hisashi Hifumi wrote:
>> Hi.
>>
>> I got following BUG trace.
>> This is violation of BUG_ON(!buffer_locked(bh)) check on submit_bh()
>> function.
>> In write_dev_supers(), if wait parameter is set and buffer_uptodate() check
>> is negative, submit_bh() is executed and hit above BUG_ON.
>> So I fixed this issue.
>
>Thanks for finding this bug and sending the patch.
>
>This function is very confusing. If wait parameter is set, it
>isn't supposed to do any IO at all. The caller first does
>write_dev_supers with wait == 0, and that sends all the supers down on
>all the devices.
>
>Then it calls again with wait == 1, which is supposed to make sure all
>the supers actually got to disk.
>
>We should change the wait == 0 behavior to leave a reference held on all
>the buffers, and wait == 1 to drop that reference. That way the buffer
>won't disappear while we are waiting, and we can return an error if the
>buffer wasn't up to date when wait == 1.
>
Like this?
I changed wait == 0 case to get extra ref and on wait == 1 case if buffer is
uptodate, bh releases ref otherwise buffer takes lock to proceed to submit_bh.
Thanks.
Signed-off-by: Hisashi Hifumi <hifumi.hisa...@oss.ntt.co.jp>
diff -Nrup linux-2.6.30-rc8.org/fs/btrfs/disk-io.c
linux-2.6.30-rc8.btrfs/fs/btrfs/disk-io.c
--- linux-2.6.30-rc8.org/fs/btrfs/disk-io.c 2009-06-04 16:26:25.000000000
+0900
+++ linux-2.6.30-rc8.btrfs/fs/btrfs/disk-io.c 2009-06-10 15:41:03.000000000
+0900
@@ -2044,8 +2044,10 @@ static int write_dev_supers(struct btrfs
wait_on_buffer(bh);
if (buffer_uptodate(bh)) {
brelse(bh);
+ brelse(bh);
continue;
- }
+ } else
+ lock_buffer(bh);
} else {
btrfs_set_super_bytenr(sb, bytenr);
@@ -2062,6 +2064,7 @@ static int write_dev_supers(struct btrfs
set_buffer_uptodate(bh);
get_bh(bh);
+ get_bh(bh);
lock_buffer(bh);
bh->b_end_io = btrfs_end_buffer_write_sync;
}
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