When adding devices that don't have a scsi_dh on a BIO based multipath,
I was able to consistently hit the warning below and lock-up the system.
The problem is that __map_bio reads the flag before it potentially being
modified by choose_pgpath, and ends up using the older value.
The WARN_ON below is not trivially linked to the issue. It goes like
this: The activate_path delayed_work is not initialized for non-scsi_dh
devices, but we always set MPATHF_QUEUE_IO, asking for initialization.
That is fine, since MPATHF_QUEUE_IO would be cleared in choose_pgpath.
Nevertheless, only for BIO-based mpath, we cache the flag before calling
choose_pgpath, and use the older version when deciding if we should
initialize the path. Therefore, we end up trying to initialize the
paths, and calling the non-initialized activate_path work.
[ 82.437100] ------------[ cut here ]------------
[ 82.437659] WARNING: CPU: 3 PID: 602 at kernel/workqueue.c:1624
__queue_delayed_work+0x71/0x90
[ 82.438436] Modules linked in:
[ 82.438911] CPU: 3 PID: 602 Comm: systemd-udevd Not tainted 5.6.0-rc6+ #339
[ 82.439680] RIP: 0010:__queue_delayed_work+0x71/0x90
[ 82.440287] Code: c1 48 89 4a 50 81 ff 00 02 00 00 75 2a 4c 89 cf e9
94 d6 07 00 e9 7f e9 ff ff 0f 0b eb c7 0f 0b 48 81 7a 58 40 74 a8 94 74
a7 <0f> 0b 48 83 7a 48 00 74 a5 0f 0b eb a1 89 fe 4c 89 cf e9 c8 c4 07
[ 82.441719] RSP: 0018:ffffb738803977c0 EFLAGS: 00010007
[ 82.442121] RAX: ffffa086389f9740 RBX: 0000000000000002 RCX: 0000000000000000
[ 82.442718] RDX: ffffa086350dd930 RSI: ffffa0863d76f600 RDI: 0000000000000200
[ 82.443484] RBP: 0000000000000200 R08: 0000000000000000 R09: ffffa086350dd970
[ 82.444128] R10: 0000000000000000 R11: 0000000000000000 R12: ffffa086350dd930
[ 82.444773] R13: ffffa0863d76f600 R14: 0000000000000000 R15: ffffa08636738008
[ 82.445427] FS: 00007f6abfe9dd40(0000) GS:ffffa0863dd80000(0000) knlGS:00000
[ 82.446040] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 82.446478] CR2: 0000557d288db4e8 CR3: 0000000078b36000 CR4: 00000000000006e0
[ 82.447104] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 82.447561] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 82.448012] Call Trace:
[ 82.448164] queue_delayed_work_on+0x6d/0x80
[ 82.448472] __pg_init_all_paths+0x7b/0xf0
[ 82.448714] pg_init_all_paths+0x26/0x40
[ 82.448980] __multipath_map_bio.isra.0+0x84/0x210
[ 82.449267] __map_bio+0x3c/0x1f0
[ 82.449468] __split_and_process_non_flush+0x14a/0x1b0
[ 82.449775] __split_and_process_bio+0xde/0x340
[ 82.450045] ? dm_get_live_table+0x5/0xb0
[ 82.450278] dm_process_bio+0x98/0x290
[ 82.450518] dm_make_request+0x54/0x120
[ 82.450778] generic_make_request+0xd2/0x3e0
[ 82.451038] ? submit_bio+0x3c/0x150
[ 82.451278] submit_bio+0x3c/0x150
[ 82.451492] mpage_readpages+0x129/0x160
[ 82.451756] ? bdev_evict_inode+0x1d0/0x1d0
[ 82.452033] read_pages+0x72/0x170
[ 82.452260] __do_page_cache_readahead+0x1ba/0x1d0
[ 82.452624] force_page_cache_readahead+0x96/0x110
[ 82.452903] generic_file_read_iter+0x84f/0xae0
[ 82.453192] ? __seccomp_filter+0x7c/0x670
[ 82.453547] new_sync_read+0x10e/0x190
[ 82.453883] vfs_read+0x9d/0x150
[ 82.454172] ksys_read+0x65/0xe0
[ 82.454466] do_syscall_64+0x4e/0x210
[ 82.454828] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[...]
[ 82.462501] ---[ end trace bb39975e9cf45daa ]---
Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
---
drivers/md/dm-mpath.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index f9b6a7a68bec..f5e7f8e88767 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -589,6 +589,11 @@ static struct pgpath *__map_bio(struct multipath *m, struct bio *bio)
if (!pgpath || !queue_io)
pgpath = choose_pgpath(m, bio->bi_iter.bi_size);
+ /*
+ * MPATHF_QUEUE_IO might have been cleared by choose_pgpath.
+ */
+ queue_io = test_bit(MPATHF_QUEUE_IO, &m->flags);
+
if ((pgpath && queue_io) ||
(!pgpath && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))) {
/* Queue for the daemon to resubmit */
--
2.26.2
--
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