[Bug 53951] New: race condition on mounting local disks with autofs

[Bug 53951] New: race condition on mounting local disks with autofs

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=53951

           Summary: race condition on mounting local disks with autofs
           Product: File System
           Version: 2.5
    Kernel Version: 3.7.7
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ext4
        AssignedTo: fs_ext4@kernel-bugs.osdl.org
        ReportedBy: harri@afaics.de
        Regression: No


I am using autofs to mount a local disk to /misc/data6 on request. Problem: It
seems that the first access silently fails, if the disk is not yet mounted.


Below is an example. Before running it I had umounted /misc/data6 and restarted
autofs.

% find /misc/data6 | wc -l; find /misc/data6 | wc -l
18
find: `/misc/data6/lost+found': Permission denied
358


As you can see, the first "find" sees just a subset of the directory entries.
The second "find" stumbles over lost+found (as expected) and finds all entries.

Kernel is 3.7.7. There is no error message in kernel.log, only a line to
mention the mount:

EXT4-fs (sdd1): mounted filesystem with ordered data mode. Opts: (null)


/etc/auto.master:
/misc   /etc/auto.misc

/etc/auto.misc:
data1   -fstype=auto,noatime    :/dev/disk/by-label/data1
data2   -fstype=auto,noatime    :/dev/disk/by-label/data2
data3   -fstype=auto,noatime    :/dev/disk/by-label/data3
data4   -fstype=auto,noatime    :/dev/disk/by-label/data4
data5   -fstype=auto,noatime    :/dev/disk/by-label/data5
data6   -fstype=auto,noatime    :/dev/disk/by-label/data6
data7   -fstype=auto,noatime    :/dev/disk/by-label/data7
data8   -fstype=auto,noatime    :/dev/disk/by-label/data8


The problem is reproducible, as it seems. Please mail if I can help to track
this down.

Regards
Harri

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[Bug 53951] race condition on mounting local disks with autofs

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=53951

--- Comment #1 from Harald Dunkel <harri@afaics.de> ---
This problem is still in (using 3.12.8):

% find /misc/data6 | wc -l; find /misc/data6 | wc -l
17
find: `/misc/data6/lost+found': Permission denied
341

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Re: [Bug 53951] race condition on mounting local disks with autofs

[Theodore Ts'o]

On Wed, Feb 05, 2014 at 05:03:53PM +0000, bugzilla-daemon@bugzilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=53951
> 
> --- Comment #1 from Harald Dunkel <harri@afaics.de> ---
> This problem is still in (using 3.12.8):
> 
> % find /misc/data6 | wc -l; find /misc/data6 | wc -l
> 17
> find: `/misc/data6/lost+found': Permission denied
> 341

Hi Harald,

There isn't an autofs bugzilla component, and it's unlikely that the
autofs folks are reading the ext4 mailing list.  Since this bug is
almost certainly an autofs problem, using bugzilla might not be the
best way to report the bug in a way that get the attention of the
right people.

I've cc'ed the autofs folks; hopefully they can help you out.

     	       	      	     	       - Ted


Original bug report, from https://bugzilla.kernel.org/show_bug.cgi?id=53951:

Harald Dunkel 2013-02-16 15:55:40 UTC

I am using autofs to mount a local disk to /misc/data6 on
request. Problem: It seems that the first access silently fails, if
the disk is not yet mounted.


Below is an example. Before running it I had umounted /misc/data6 and
restarted autofs.

% find /misc/data6 | wc -l; find /misc/data6 | wc -l
18
find: `/misc/data6/lost+found': Permission denied
358


As you can see, the first "find" sees just a subset of the directory
entries. The second "find" stumbles over lost+found (as expected) and
finds all entries.

Kernel is 3.7.7. There is no error message in kernel.log, only a line
to mention the mount:

EXT4-fs (sdd1): mounted filesystem with ordered data mode. Opts: (null)


/etc/auto.master:
/misc   /etc/auto.misc

/etc/auto.misc:
data1   -fstype=auto,noatime    :/dev/disk/by-label/data1
data2   -fstype=auto,noatime    :/dev/disk/by-label/data2
data3   -fstype=auto,noatime    :/dev/disk/by-label/data3
data4   -fstype=auto,noatime    :/dev/disk/by-label/data4
data5   -fstype=auto,noatime    :/dev/disk/by-label/data5
data6   -fstype=auto,noatime    :/dev/disk/by-label/data6
data7   -fstype=auto,noatime    :/dev/disk/by-label/data7
data8   -fstype=auto,noatime    :/dev/disk/by-label/data8


The problem is reproducible, as it seems. Please mail if I can help to track this down.

Regards
Harri

Re: [Bug 53951] race condition on mounting local disks with autofs

[Ian Kent]

On Wed, 2014-02-05 at 12:49 -0500, Theodore Ts'o wrote:
> Original bug report, from https://bugzilla.kernel.org/show_bug.cgi?id=53951:
> 
> Harald Dunkel 2013-02-16 15:55:40 UTC
> 
> I am using autofs to mount a local disk to /misc/data6 on
> request. Problem: It seems that the first access silently fails, if
> the disk is not yet mounted.

Does it!

Or is it the mix of system calls that are made, some of which won't
trigger the mount and others that will. I know from experience that
find(1) does a fairly unusual mix of these calls.

Does it still happen if you append a "/" to /misc/data6.

Since there are a number of system calls that won't trigger mounts,
which is required to avoid mount storms, there needs to be some way to
selectively force mount triggering and appending a "/" to a path is the
way it's done (at least it should function that way).

Mind you the mix of calls won't matter if the automount is mounted
"nobrowse" since mount point directories that don't yet exist should
trigger a mount on any access.

The default installed autofs configuration sets this but if you wiped
out the configuration and didn't retain that setting then the automount
will be mounted "browse", the internal program default.

What are you using for that setting?

Ian

[Bug 53951] race condition on mounting local disks with autofs

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=53951

--- Comment #2 from Theodore Tso <tytso@mit.edu> ---
On Wed, Feb 05, 2014 at 05:03:53PM +0000, bugzilla-daemon@bugzilla.kernel.org
wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=53951
> 
> --- Comment #1 from Harald Dunkel <harri@afaics.de> ---
> This problem is still in (using 3.12.8):
> 
> % find /misc/data6 | wc -l; find /misc/data6 | wc -l
> 17
> find: `/misc/data6/lost+found': Permission denied
> 341

Hi Harald,

There isn't an autofs bugzilla component, and it's unlikely that the
autofs folks are reading the ext4 mailing list.  Since this bug is
almost certainly an autofs problem, using bugzilla might not be the
best way to report the bug in a way that get the attention of the
right people.

I've cc'ed the autofs folks; hopefully they can help you out.

                                              - Ted


Original bug report, from https://bugzilla.kernel.org/show_bug.cgi?id=53951:

Harald Dunkel 2013-02-16 15:55:40 UTC

I am using autofs to mount a local disk to /misc/data6 on
request. Problem: It seems that the first access silently fails, if
the disk is not yet mounted.


Below is an example. Before running it I had umounted /misc/data6 and
restarted autofs.

% find /misc/data6 | wc -l; find /misc/data6 | wc -l
18
find: `/misc/data6/lost+found': Permission denied
358


As you can see, the first "find" sees just a subset of the directory
entries. The second "find" stumbles over lost+found (as expected) and
finds all entries.

Kernel is 3.7.7. There is no error message in kernel.log, only a line
to mention the mount:

EXT4-fs (sdd1): mounted filesystem with ordered data mode. Opts: (null)


/etc/auto.master:
/misc   /etc/auto.misc

/etc/auto.misc:
data1   -fstype=auto,noatime    :/dev/disk/by-label/data1
data2   -fstype=auto,noatime    :/dev/disk/by-label/data2
data3   -fstype=auto,noatime    :/dev/disk/by-label/data3
data4   -fstype=auto,noatime    :/dev/disk/by-label/data4
data5   -fstype=auto,noatime    :/dev/disk/by-label/data5
data6   -fstype=auto,noatime    :/dev/disk/by-label/data6
data7   -fstype=auto,noatime    :/dev/disk/by-label/data7
data8   -fstype=auto,noatime    :/dev/disk/by-label/data8


The problem is reproducible, as it seems. Please mail if I can help to track
this down.

Regards
Harri

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You are watching the assignee of the bug.

[Bug 53951] race condition on mounting local disks with autofs

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=53951

--- Comment #3 from Ian Kent <raven@themaw.net> ---
On Wed, 2014-02-05 at 12:49 -0500, Theodore Ts'o wrote:
> Original bug report, from https://bugzilla.kernel.org/show_bug.cgi?id=53951:
> 
> Harald Dunkel 2013-02-16 15:55:40 UTC
> 
> I am using autofs to mount a local disk to /misc/data6 on
> request. Problem: It seems that the first access silently fails, if
> the disk is not yet mounted.

Does it!

Or is it the mix of system calls that are made, some of which won't
trigger the mount and others that will. I know from experience that
find(1) does a fairly unusual mix of these calls.

Does it still happen if you append a "/" to /misc/data6.

Since there are a number of system calls that won't trigger mounts,
which is required to avoid mount storms, there needs to be some way to
selectively force mount triggering and appending a "/" to a path is the
way it's done (at least it should function that way).

Mind you the mix of calls won't matter if the automount is mounted
"nobrowse" since mount point directories that don't yet exist should
trigger a mount on any access.

The default installed autofs configuration sets this but if you wiped
out the configuration and didn't retain that setting then the automount
will be mounted "browse", the internal program default.

What are you using for that setting?

Ian

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[Bug 53951] race condition on mounting local disks with autofs

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=53951

Harald Dunkel <harri@afaics.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from Harald Dunkel <harri@afaics.de> ---
Hi folks,

using "/misc/data6/" or a manual mount or BROWSE_MODE=no did the trick, so it
seems you are right. I will contact the autofs folks. 

Thanx very much 
Harri

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