Dear Linux folks,


Am 20.03.21 um 00:00 schrieb Song Liu:

On Wed, Feb 24, 2021 at 1:26 AM Guoqing Jiang wrote:

quoted

On 2/24/21 10:09, Song Liu wrote:

quoted

On Mon, Feb 15, 2021 at 3:08 AM Paul Menzel wrote:

quoted

[+cc Donald]

Am 13.02.21 um 01:49 schrieb Guoqing Jiang:

quoted

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:
https://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@molgen.mpg.de/T/#t (local)

And add one parameter to md_reap_sync_thread since it could be called by
dm-raid which doesn't hold reconfig_mutex.

Reported-and-tested-by: Donald Buczek <redacted>
Signed-off-by: Guoqing Jiang <redacted>

I don't really like this fix. But I haven't got a better (and not too
complicated)
alternative.

quoted

quoted

---
V2:
1. add one parameter to md_reap_sync_thread per Jack's suggestion.

    drivers/md/dm-raid.c |  2 +-
    drivers/md/md.c      | 14 +++++++++-----
    drivers/md/md.h      |  2 +-
    3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index cab12b2..0c4cbba 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c

@@ -3668,7 +3668,7 @@ static int raid_message(struct dm_target *ti, unsigned int argc, char **argv,
        if (!strcasecmp(argv[0], "idle") || !strcasecmp(argv[0], "frozen")) {
                if (mddev->sync_thread) {
                        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-                     md_reap_sync_thread(mddev);
+                     md_reap_sync_thread(mddev, false);

I think we can add mddev_lock() and mddev_unlock() here and then we don't
need the extra parameter?

I thought it too, but I would prefer get the input from DM people first.

@ Mike or Alasdair

Hi Mike and Alasdair,

Could you please comment on this option: adding mddev_lock() and mddev_unlock()
to raid_message() around md_reap_sync_thread()?

The issue is unfortunately still unresolved (at least Linux 5.10.82). 
How can we move forward?


Kind regards,

Paul