(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.
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?
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?
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