Andrew Morton wrote:
> (cc's added)
>
> On Mon, 05 Jan 2009 11:23:33 +0800 Li Zefan <lizf@xxxxxxxxxxxxxx> wrote:
>
>> Thread 1:
>> for ((; ;))
>> {
>> mount -t cgroup -o cpuset xxx /mnt > /dev/null 2>&1
>> mkdir /mnt/0 > /dev/null 2>&1
>> rmdir /mnt/0 > /dev/null 2>&1
>> umount /mnt > /dev/null 2>&1
>> }
>>
>> Thread 2:
>> for ((; ;))
>> {
>> mount -t cpuset xxx /mnt > /dev/null 2>&1
>> umount /mnt > /dev/null 2>&1
>> }
>>
>> (Note: Again it is irrelevant which cgroup subsys is used.)
>>
>> After a while this showed up:
>>
>> ------------[ cut here ]------------
>> WARNING: at fs/namespace.c:636 mntput_no_expire+0xac/0xf2()
>> Hardware name: Aspire SA85
>> Modules linked in: bridge stp llc autofs4 dm_mirror dm_region_hash dm_log dm_mod r8169 parport_pc mii parport sg button sata_sis pata_sis ata_generic libata sd_mod scsi_mod ext3 jbd mbcache uhci_hcd ohci_hcd ehci_hcd [last unloaded: scsi_wait_scan]
>> Pid: 4745, comm: umount Not tainted 2.6.28 #479
>> Call Trace:
>> [<c042bbe3>] warn_slowpath+0x79/0x8f
>> [<c044babf>] ? __lock_acquire+0x69a/0x700
>> [<c04ae44e>] ? mntput_no_expire+0x79/0xf2
>> [<c04ae481>] mntput_no_expire+0xac/0xf2
>> [<c04ae968>] sys_umount+0x26a/0x2b1
>> [<c04ae9c1>] sys_oldumount+0x12/0x14
>> [<c0403251>] sysenter_do_call+0x12/0x31
>> ---[ end trace 79d0ab4bef01333f ]---
>>
>> The WARNING is: WARN_ON(atomic_read(&mnt->__mnt_writers));
>
> OK, I'm all confused. Here we see a WARN_ON triggered, but in
> http://lkml.org/lkml/2009/1/4/352 with the same testcase we're seeing a
> lockdep warning.
>
They are 2 testcases with small difference ;)
case 1:
mount
cat whichever control file
umount
case 2:
mount
mkdir /cgroup/0
rmdir /cgroup/0
umount
> You refer to Arjan's "lockdep: annotate sb ->s_umount" patch - but
> that's over two years old.
>
> And you say "The changelog said s_umount needs to be classified as
> per-sb, but actually it made it as per-filesystem." But what is the
> difference between per-sb and per-fs?
>
a filesystem can be single-sb or multile, isn't it? that's struct super_lock
and struct file_system_type. I may be wrong here, since I don't know
much about VFS...
> More info here: http://bugzilla.kernel.org/show_bug.cgi?id=12673
>
> This bug report seems to be all over the place.
>
> Is it a post-2.6.28 regression, btw?
>
I think it was introduced since cgroup was introduced. But it's hard to trigger
in real-life, though it's easy using this test case.
_______________________________________________
Containers mailing list
Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linux-foundation.org/mailman/listinfo/containers
