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@wdc.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: Kees Cook keescook@chromium.org Cc: David Windsor dwindsor@gmail.com Cc: Hans Liljestrand ishkamiel@gmail.com Cc: Hannes Reinecke hare@suse.com Cc: stable@vger.kernel.org # 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;