[PATCH v2] Remove: container should wait for an array to release a drive

[PATCH v2] Remove: container should wait for an array to release a drive

[Tomasz Majchrzak]

A 'faulty' drive is being removed from a container after it has been
released by an array, however there is a race there. The drive is
released asynchronously by a monitor but sometimes it doesn't happen
before container checks it. It results in a container refusing to remove
a drive as it still seems to be a part of some array.

It seems 'ping_monitor' could be a solution here to assure monitor has
had a chance to process the events, however it doesn't resolve the
problem - sometimes an array has to request a release of the drive few
times (as the array is busy) and single 'ping_monitor' call is not
sufficient. As there is no way to query monitor progress, it forces us
to retry a check several times before an error is returned.

Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com>
---
 Manage.c | 38 +++++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/Manage.c b/Manage.c
index e2e88b8..7f8eb88 100644
--- a/Manage.c
+++ b/Manage.c
@@ -1125,19 +1125,31 @@ int Manage_remove(struct supertype *tst, int fd, struct mddev_dev *dv,
 		 */
 		if (rdev == 0)
 			ret = -1;
-		else
-			ret = sysfs_unique_holder(devnm, rdev);
-		if (ret == 0) {
-			pr_err("%s is not a member, cannot remove.\n",
-			       dv->devname);
-			close(lfd);
-			return -1;
-		}
-		if (ret >= 2) {
-			pr_err("%s is still in use, cannot remove.\n",
-			       dv->devname);
-			close(lfd);
-			return -1;
+		else {
+			/* The drive has already been set to 'faulty', however monitor might
+			 * not have had time to process it and the drive might still have
+			 * an entry in the 'holders' directory. Try a few times to avoid
+			 * a false error */
+			int count = 20;
+			do {
+				ret = sysfs_unique_holder(devnm, rdev);
+				if (ret < 2)
+					break;
+				usleep(100 * 1000);	//100ms
+			} while (--count > 0);
+
+			if (ret == 0) {
+				pr_err("%s is not a member, cannot remove.\n",
+					dv->devname);
+				close(lfd);
+				return -1;
+			}
+			if (ret >= 2) {
+				pr_err("%s is still in use, cannot remove.\n",
+					dv->devname);
+				close(lfd);
+				return -1;
+			}
 		}
 	}
 	/* FIXME check that it is a current member */
-- 
1.8.3.1

Re: [PATCH v2] Remove: container should wait for an array to release a drive

[Jes Sorensen]

Tomasz Majchrzak <tomasz.majchrzak@intel.com> writes:
> A 'faulty' drive is being removed from a container after it has been
> released by an array, however there is a race there. The drive is
> released asynchronously by a monitor but sometimes it doesn't happen
> before container checks it. It results in a container refusing to remove
> a drive as it still seems to be a part of some array.
>
> It seems 'ping_monitor' could be a solution here to assure monitor has
> had a chance to process the events, however it doesn't resolve the
> problem - sometimes an array has to request a release of the drive few
> times (as the array is busy) and single 'ping_monitor' call is not
> sufficient. As there is no way to query monitor progress, it forces us
> to retry a check several times before an error is returned.
>
> Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com>
> ---
>  Manage.c | 38 +++++++++++++++++++++++++-------------
>  1 file changed, 25 insertions(+), 13 deletions(-)
>
> diff --git a/Manage.c b/Manage.c
> index e2e88b8..7f8eb88 100644
> --- a/Manage.c
> +++ b/Manage.c
> @@ -1125,19 +1125,31 @@ int Manage_remove(struct supertype *tst, int fd, struct mddev_dev *dv,
>  		 */
>  		if (rdev == 0)
>  			ret = -1;
> -		else
> -			ret = sysfs_unique_holder(devnm, rdev);
> -		if (ret == 0) {
> -			pr_err("%s is not a member, cannot remove.\n",
> -			       dv->devname);
> -			close(lfd);
> -			return -1;
> -		}
> -		if (ret >= 2) {
> -			pr_err("%s is still in use, cannot remove.\n",
> -			       dv->devname);
> -			close(lfd);
> -			return -1;
> +		else {
> +			/* The drive has already been set to 'faulty', however monitor might
> +			 * not have had time to process it and the drive might still have
> +			 * an entry in the 'holders' directory. Try a few times to avoid
> +			 * a false error */

Sorry for nagging again, but code is 80 characters wide, and comments
should not go beyond the 80 character limit - just like in the
kernel. The preferred format is (with applicable indentation):

/*
 * Blah blah blah blah blah
 * .... more blah blah blah
 */

Thanks,
Jes