[ 023/100] dm: do not replace bioset for request based dm

From: Greg Kroah-Hartman
Date: Tue Mar 12 2013 - 19:19:39 EST

3.8-stable review patch. If anyone has any objections, please let me know.


From: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>

commit 16245bdc9d3e22d1460341a655c8b5288953bc14 upstream.

This patch fixes a regression introduced in v3.8, which causes oops
like this when dm-multipath is used:

general protection fault: 0000 [#1] SMP
RIP: 0010:[<ffffffff810fe754>] [<ffffffff810fe754>] mempool_free+0x24/0xb0
Call Trace:
[<ffffffff81187417>] bio_put+0x97/0xc0
[<ffffffffa02247a5>] end_clone_bio+0x35/0x90 [dm_mod]
[<ffffffff81185efd>] bio_endio+0x1d/0x30
[<ffffffff811f03a3>] req_bio_endio.isra.51+0xa3/0xe0
[<ffffffff811f2f68>] blk_update_request+0x118/0x520
[<ffffffff811f3397>] blk_update_bidi_request+0x27/0xa0
[<ffffffff811f343c>] blk_end_bidi_request+0x2c/0x80
[<ffffffff811f34d0>] blk_end_request+0x10/0x20
[<ffffffffa000b32b>] scsi_io_completion+0xfb/0x6c0 [scsi_mod]
[<ffffffffa000107d>] scsi_finish_command+0xbd/0x120 [scsi_mod]
[<ffffffffa000b12f>] scsi_softirq_done+0x13f/0x160 [scsi_mod]
[<ffffffff811f9fd0>] blk_done_softirq+0x80/0xa0
[<ffffffff81044551>] __do_softirq+0xf1/0x250
[<ffffffff8142ee8c>] call_softirq+0x1c/0x30
[<ffffffff8100420d>] do_softirq+0x8d/0xc0
[<ffffffff81044885>] irq_exit+0xd5/0xe0
[<ffffffff8142f3e3>] do_IRQ+0x63/0xe0
[<ffffffff814257af>] common_interrupt+0x6f/0x6f
[<ffffffffa021737c>] srp_queuecommand+0x8c/0xcb0 [ib_srp]
[<ffffffffa0002f18>] scsi_dispatch_cmd+0x148/0x310 [scsi_mod]
[<ffffffffa000a38e>] scsi_request_fn+0x31e/0x520 [scsi_mod]
[<ffffffff811f1e57>] __blk_run_queue+0x37/0x50
[<ffffffff811f1f69>] blk_delay_work+0x29/0x40
[<ffffffff81059003>] process_one_work+0x1c3/0x5c0
[<ffffffff8105b22e>] worker_thread+0x15e/0x440
[<ffffffff8106164b>] kthread+0xdb/0xe0
[<ffffffff8142db9c>] ret_from_fork+0x7c/0xb0

The regression was introduced by the change
c0820cf5 "dm: introduce per_bio_data", where dm started to replace
bioset during table replacement.
For bio-based dm, it is good because clone bios do not exist during the
table replacement.
For request-based dm, however, (not-yet-mapped) clone bios may stay in
request queue and survive during the table replacement.
So freeing the old bioset could cause the oops in bio_put().

Since the size of front_pad may change only with bio-based dm,
it is not necessary to replace bioset for request-based dm.

Reported-by: Bart Van Assche <bvanassche@xxxxxxx>
Tested-by: Bart Van Assche <bvanassche@xxxxxxx>
Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
Acked-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Acked-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/md/dm.c | 30 +++++++++++++++++++++---------
1 file changed, 21 insertions(+), 9 deletions(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1973,15 +1973,27 @@ static void __bind_mempools(struct mappe
struct dm_md_mempools *p = dm_table_get_md_mempools(t);

- if (md->io_pool && (md->tio_pool || dm_table_get_type(t) == DM_TYPE_BIO_BASED) && md->bs) {
- /*
- * The md already has necessary mempools. Reload just the
- * bioset because front_pad may have changed because
- * a different table was loaded.
- */
- bioset_free(md->bs);
- md->bs = p->bs;
- p->bs = NULL;
+ if (md->io_pool && md->bs) {
+ /* The md already has necessary mempools. */
+ if (dm_table_get_type(t) == DM_TYPE_BIO_BASED) {
+ /*
+ * Reload bioset because front_pad may have changed
+ * because a different table was loaded.
+ */
+ bioset_free(md->bs);
+ md->bs = p->bs;
+ p->bs = NULL;
+ } else if (dm_table_get_type(t) == DM_TYPE_REQUEST_BASED) {
+ BUG_ON(!md->tio_pool);
+ /*
+ * There's no need to reload with request-based dm
+ * because the size of front_pad doesn't change.
+ * Note for future: If you are to reload bioset,
+ * prep-ed requests in the queue may refer
+ * to bio from the old bioset, so you must walk
+ * through the queue to unprep.
+ */
+ }
goto out;

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