On 2/11/21 08:28, Song Liu wrote:
On Tue, Feb 9, 2021 at 6:22 PM Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx> wrote:Unregister sync_thread doesn't need to hold reconfig_mutex since it doesn't reconfigure array. And it could cause deadlock problem for raid5 as follows: 1. process A tried to reap sync thread with reconfig_mutex held after echo idle to sync_action. 2. raid5 sync thread was blocked if there were too many active stripes. 3. SB_CHANGE_PENDING was set (because of write IO comes from upper layer) which causes the number of active stripes can't be decreased. 4. SB_CHANGE_PENDING can't be cleared since md_check_recovery was not able to hold reconfig_mutex. More details in the link: issu://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@xxxxxxxxxxxxx/T/#t Reported-and-tested-by: Donald Buczek <buczek@xxxxxxxxxxxxx> Signed-off-by: Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx>Thanks for debugging the issue. However, I am not sure whether this is the proper fix. For example, would this break dm-raid.c:raid_message()? IIUC, raid_message() calls md_reap_sync_thread() without holding reconfigure_mutex, no?
Oops, I didn't notice dm-raid calls it though md did call it with reconfig_mutex held. But on the other side, it proves we don't need to call md_reap_sync_thread with the mutex held.
Thanks, Guoqing
