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  1. 23 5月, 2017 2 次提交
    • E
      mnt: In propgate_umount handle visiting mounts in any order · 99b19d16
      由 Eric W. Biederman 提交于 
      While investigating some poor umount performance I realized that in
the case of overlapping mount trees where some of the mounts are locked
the code has been failing to unmount all of the mounts it should
have been unmounting.

This failure to unmount all of the necessary
mounts can be reproduced with:

$ cat locked_mounts_test.sh

mount -t tmpfs test-base /mnt
mount --make-shared /mnt
mkdir -p /mnt/b

mount -t tmpfs test1 /mnt/b
mount --make-shared /mnt/b
mkdir -p /mnt/b/10

mount -t tmpfs test2 /mnt/b/10
mount --make-shared /mnt/b/10
mkdir -p /mnt/b/10/20

mount --rbind /mnt/b /mnt/b/10/20

unshare -Urm --propagation unchaged /bin/sh -c 'sleep 5; if [ $(grep test /proc/self/mountinfo | wc -l) -eq 1 ] ; then echo SUCCESS ; else echo FAILURE ; fi'
sleep 1
umount -l /mnt/b
wait %%

$ unshare -Urm ./locked_mounts_test.sh

This failure is corrected by removing the prepass that marks mounts
that may be umounted.

A first pass is added that umounts mounts if possible and if not sets
mount mark if they could be unmounted if they weren't locked and adds
them to a list to umount possibilities.  This first pass reconsiders
the mounts parent if it is on the list of umount possibilities, ensuring
that information of umoutability will pass from child to mount parent.

A second pass then walks through all mounts that are umounted and processes
their children unmounting them or marking them for reparenting.

A last pass cleans up the state on the mounts that could not be umounted
and if applicable reparents them to their first parent that remained
mounted.

While a bit longer than the old code this code is much more robust
as it allows information to flow up from the leaves and down
from the trunk making the order in which mounts are encountered
in the umount propgation tree irrelevant.

Cc: stable@vger.kernel.org
Fixes: 0c56fe31 ("mnt: Don't propagate unmounts to locked mounts")
Reviewed-by: NAndrei Vagin <avagin@virtuozzo.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      99b19d16
    • E
      mnt: In umount propagation reparent in a separate pass · 570487d3
      由 Eric W. Biederman 提交于 
      It was observed that in some pathlogical cases that the current code
does not unmount everything it should.  After investigation it
was determined that the issue is that mnt_change_mntpoint can
can change which mounts are available to be unmounted during mount
propagation which is wrong.

The trivial reproducer is:
$ cat ./pathological.sh

mount -t tmpfs test-base /mnt
cd /mnt
mkdir 1 2 1/1
mount --bind 1 1
mount --make-shared 1
mount --bind 1 2
mount --bind 1/1 1/1
mount --bind 1/1 1/1
echo
grep test-base /proc/self/mountinfo
umount 1/1
echo
grep test-base /proc/self/mountinfo

$ unshare -Urm ./pathological.sh

The expected output looks like:
46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000
47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
49 54 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
50 53 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
51 49 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
54 47 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
53 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
52 50 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000

46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000
47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000

The output without the fix looks like:
46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000
47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
49 54 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
50 53 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
51 49 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
54 47 0:25 /1/1 /mnt/1/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
53 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
52 50 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000

46 31 0:25 / /mnt rw,relatime - tmpfs test-base rw,uid=1000,gid=1000
47 46 0:25 /1 /mnt/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
48 46 0:25 /1 /mnt/2 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000
52 48 0:25 /1/1 /mnt/2/1 rw,relatime shared:1 - tmpfs test-base rw,uid=1000,gid=1000

That last mount in the output was in the propgation tree to be unmounted but
was missed because the mnt_change_mountpoint changed it's parent before the walk
through the mount propagation tree observed it.

Cc: stable@vger.kernel.org
Fixes: 1064f874 ("mnt: Tuck mounts under others instead of creating shadow/side mounts.")
Acked-by: NAndrei Vagin <avagin@virtuozzo.com>
Reviewed-by: NRam Pai <linuxram@us.ibm.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      570487d3
  3. 13 5月, 2017 6 次提交
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  9. 09 5月, 2017 26 次提交