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Avoid lazy umount MNT_DETACH for NFS mounts as this causes system hang #47

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Avoid lazy umount MNT_DETACH for NFS mounts as this causes system hang #47

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563d28c
Avoid lazy umount MNT_DETACH for NFS mounts as this causes system hang
rhmcruiser Mar 5, 2020
5956b37
cleaned up my earlier commit's mistake
rhmcruiser Mar 22, 2020
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28 changes: 25 additions & 3 deletions src/oci-umount.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@
#include <linux/limits.h>
#include <yajl/yajl_tree.h>
#include <ctype.h>

#include <sys/statfs.h>
#include "config.h"

#define _cleanup_(x) __attribute__((cleanup(x)))
Expand Down Expand Up @@ -684,7 +684,15 @@ static int unmount(const char *id, char *umount_path, bool submounts_only, const
return 0;
}

ret = umount2(umount_path, MNT_DETACH);
/* Here dont lazy umount NFS filesystem f_type : NFS_SUPER_MAGIC 0x6969 */
if ( (statfs(umount_path, &fs) != 0)
pr_perror("statfs of %s failed \n");

if (fs.f_type == 0x6969)
ret = umount(umount_path);
else
ret = umount2(umount_path, MNT_DETACH);

if (!ret)
pr_pinfo("%s: Unmounted: [%s]", id, umount_path);
else
Expand Down Expand Up @@ -722,7 +730,21 @@ static int unmount(const char *id, char *umount_path, bool submounts_only, const
continue;
}

ret = umount2(mnt_table[i].destination, MNT_DETACH);
/*
Here DONT lazy unmount for NFS mounts as it causes serious problems of hung tasks which are doing NFS IO,
we see them in vmcore in UNinterruptible state and also will be hung indefinitely. In some cases we have
seen the NFS IO tasks in blocked UN state not even allowing the reboot/shutdown task to progress as the
shutdown gets into blocked UNinterruptile state waiting for NFS superblock synching of inodes before shutdown.
But the NFS tasks wont progress and are blocked waiting because the network interfaces were already down by this
stage and NFS IO is held up. Although the lazy umount removes it from the mount table we have seen the superblock.s_count
and s_active reflecting it in use and holding the number of refernces by several tasks for NFS IO.
*/

if (fs.f_type == 0x6969)
ret = umount(mnt_table[i].destination);
else
ret = umount2(mnt_table[i].destination, MNT_DETACH);

if (!ret)
pr_pinfo("%s: Unmounted submount: [%s]", id, mnt_table[i].destination);
else
Expand Down