[Devel] [PATCH RHEL9 COMMIT] dm/push_backup: Allow to stop push_backup at any time

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.0-162.6.1.vz9.18.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh9-5.14.0-162.6.1.vz9.18.11
------>
commit 845cd8f772fc7e1ce34b7a910eff6a99d005cd24
Author: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
Date:   Mon Feb 13 19:36:43 2023 +0300

    dm/push_backup: Allow to stop push_backup at any time
    
    Currently push_backup device cannot be stopped if any process
    in a system is waiting next push block via push_backup_read.
    This means we have to kill that process or thread to release
    push_backup device, as it holds pb->ctl_rwsem.
    
    Change code so push_backup is marked !alive and all waiters are
    woken up before acquiring the lock. This is safe to do as pb->alive
    is only used for determining if we should postpone new I/O and
    process user push_backup_read/push_backup_write. All operations
    like releasing I/O or memory will be done with acquired lock as
    soon as all kicked readers exit syscall.
    
    https://jira.sw.ru/browse/PSBM-145865
    Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
    
    Feature: dm-backup: push backup target driver
---
 drivers/md/dm-push-backup.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-push-backup.c b/drivers/md/dm-push-backup.c
index b0e9e78f021a..370bd23a70ff 100644
--- a/drivers/md/dm-push-backup.c
+++ b/drivers/md/dm-push-backup.c
@@ -574,6 +574,17 @@ static int pb_message(struct dm_target *ti, unsigned int argc, char **argv,
 	if (argc < 1)
 		goto out;
 
+	if (!strcmp(argv[0], "push_backup_stop")) {
+		if (argc != 1)
+			goto out;
+
+		if (!pb->map)
+			return -EBADF;
+
+		pb->alive = false;
+		wake_up_interruptible(&pb->waitq); /* pb->alive = false */
+	}
+
 	write = msg_wants_down_write(argv[0]);
 	if (write)
 		ret = down_write_killable(&pb->ctl_rwsem);
@@ -592,8 +603,6 @@ static int pb_message(struct dm_target *ti, unsigned int argc, char **argv,
 			goto unlock;
 		ret = push_backup_start(pb, val, (void *)val2);
 	} else if (!strcmp(argv[0], "push_backup_stop")) {
-		if (argc != 1)
-			goto unlock;
 		ret = push_backup_stop(pb, result, maxlen);
 	} else if (!strcmp(argv[0], "push_backup_read")) {
 		if (argc != 1)