Currently when improperly aligned discard request is submitted, we just
silently discard more / less data which results in filesystem corruption
in some cases. Refuse such misaligned requests.
Signed-off-by: Jan Kara <[email protected]>
---
drivers/block/brd.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index b9794aeeb878..4ef4cdf67ede 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -337,6 +337,9 @@ static void brd_make_request(struct request_queue *q, struct bio *bio)
goto io_error;
if (unlikely(bio->bi_rw & REQ_DISCARD)) {
+ if (sector & ((PAGE_SIZE >> SECTOR_SHIFT) - 1) ||
+ bio->bi_iter.bi_size & PAGE_MASK)
+ goto io_error;
discard_from_brd(brd, sector, bio->bi_iter.bi_size);
goto out;
}
--
2.1.4
> -----Original Message-----
> From: [email protected] [mailto:linux-kernel-
> [email protected]] On Behalf Of Jan Kara
> Sent: Wednesday, November 4, 2015 10:14 AM
> To: [email protected]
> Cc: LKML <[email protected]>; [email protected];
> Christoph Hellwig <[email protected]>; Jan Kara <[email protected]>
> Subject: [PATCH] brd: Refuse improperly aligned discard requests
>
> Currently when improperly aligned discard request is submitted, we just
> silently discard more / less data which results in filesystem corruption
> in some cases. Refuse such misaligned requests.
I agree discarding more than requested is very bad.
If they are routed to SCSI or ATA devices, though, the discard commands
(SCSI UNMAP or ATA DATA SET MANAGEMENT/TRIM) are just hints, so there
is no guarantee the discard will do anything. Are you finding
filesystems that still don't understand that? dm-raid held that
mistaken assumption for a long time.
---
Robert Elliott, HP Server Storage
On Thu 05-11-15 04:18:49, Elliott, Robert (Persistent Memory) wrote:
>
> > -----Original Message-----
> > From: [email protected] [mailto:linux-kernel-
> > [email protected]] On Behalf Of Jan Kara
> > Sent: Wednesday, November 4, 2015 10:14 AM
> > To: [email protected]
> > Cc: LKML <[email protected]>; [email protected];
> > Christoph Hellwig <[email protected]>; Jan Kara <[email protected]>
> > Subject: [PATCH] brd: Refuse improperly aligned discard requests
> >
> > Currently when improperly aligned discard request is submitted, we just
> > silently discard more / less data which results in filesystem corruption
> > in some cases. Refuse such misaligned requests.
>
> I agree discarding more than requested is very bad.
>
> If they are routed to SCSI or ATA devices, though, the discard commands
> (SCSI UNMAP or ATA DATA SET MANAGEMENT/TRIM) are just hints, so there
> is no guarantee the discard will do anything. Are you finding
> filesystems that still don't understand that? dm-raid held that
> mistaken assumption for a long time.
So there is blkdev_issue_zeroout() which uses blkdev_issue_discard() if
'discard_zeroes_data' is set. I'd hope that in that case zeroing really
happens as submitted or error is returned... Filesystems definitely depend
on blkdev_issue_zeroout() doing what it is told.
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
On 11/04/2015 09:13 AM, Jan Kara wrote:
> Currently when improperly aligned discard request is submitted, we just
> silently discard more / less data which results in filesystem corruption
> in some cases. Refuse such misaligned requests.
Applied, thanks Jan.
--
Jens Axboe