This patch avoids that the following message occurs sporadically
in the system log (revealing that pgpath->path.dev->name became
a dangling pointer):
device-mapper: table: 254:2: device kkkkkkkkkkkkkkkkkkk?????????x0?a?????E??????????????E??????F?????2?????pF??????PF?????9[F??????]F???????#???????#??????'f????? not in table devices list
This patch also fixes the following kernel crash:
general protection fault: 0000 [#1] PREEMPT SMP
RIP: 0010:multipath_busy+0x77/0xd0 [dm_multipath]
Call Trace:
dm_mq_queue_rq+0x44/0x110 [dm_mod]
blk_mq_dispatch_rq_list+0x73/0x440
blk_mq_do_dispatch_sched+0x60/0xe0
blk_mq_sched_dispatch_requests+0x11a/0x1a0
__blk_mq_run_hw_queue+0x11f/0x1c0
__blk_mq_delay_run_hw_queue+0x95/0xe0
blk_mq_run_hw_queue+0x25/0x80
blk_mq_flush_plug_list+0x197/0x420
blk_flush_plug_list+0xe4/0x270
blk_finish_plug+0x27/0x40
__do_page_cache_readahead+0x2b4/0x370
force_page_cache_readahead+0xb4/0x110
generic_file_read_iter+0x755/0x970
__vfs_read+0xd2/0x140
vfs_read+0x9b/0x140
SyS_read+0x45/0xa0
do_syscall_64+0x56/0x1a0
entry_SYSCALL64_slow_path+0x25/0x25
>From the disassembly of multipath_busy (0x77 = 119):
./include/linux/blkdev.h:
992 return bdev->bd_disk->queue; /* this is never NULL */
0x00000000000006b4 <+116>: mov (%rax),%rax
0x00000000000006b7 <+119>: mov 0xe0(%rax),%rax
Fixes: commit 2a0b4682e09d ("dm: convert dm_dev_internal.count from atomic_t to refcount_t")
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: David Windsor <dwindsor@xxxxxxxxx>
Cc: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v4.15
---
drivers/md/dm-table.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 88130b5d95f9..ee5c389e7256 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -459,6 +459,8 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
if (r)
return r;
refcount_inc(&dd->count);
+ } else {
+ refcount_inc(&dd->count);
}
*result = dd->dm_dev;
--
2.15.1
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