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    SubjectRe: autofs4 hang in 2.6.37-rc1
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    On Sun, 2010-11-14 at 17:34 +0200, Avi Kivity wrote:
    > On 11/14/2010 05:15 PM, Arnd Bergmann wrote:
    > > On Sunday 14 November 2010 14:51:04 Avi Kivity wrote:
    > > > automount S ffff88012a28a680 0 399 1 0x00000000
    > > > ffff88012a07bd08 0000000000000082 0000000000000000 0000000000000000
    > > > ffff88012a07a010 ffff88012a07bfd8 0000000000011800 ffff88012693c260
    > > > ffff88012693c5d0 ffff88012693c5c8 0000000000011800 0000000000011800
    > > > Call Trace:
    > > > [<ffffffff81056197>] ? prepare_to_wait+0x67/0x74
    > > > [<ffffffff811b23eb>] autofs4_wait+0x5a4/0x6d5
    > > > [<ffffffff81055f25>] ? autoremove_wake_function+0x0/0x34
    > > > [<ffffffff811b2ba5>] autofs4_do_expire_multi+0x5b/0xa3
    > > > [<ffffffff811b2c39>] autofs4_expire_multi+0x4c/0x54
    > > > [<ffffffff811b1750>] autofs4_root_ioctl_unlocked+0x23e/0x252
    > > > [<ffffffff811b1808>] autofs4_root_ioctl+0x39/0x53
    > > > [<ffffffff810f5e5c>] do_vfs_ioctl+0x557/0x5bb
    > > > [<ffffffff810ca644>] ? remove_vma+0x6e/0x76
    > > > [<ffffffff810cb6a2>] ? do_munmap+0x31c/0x33e
    > > > [<ffffffff810f5f02>] sys_ioctl+0x42/0x65
    > > > [<ffffffff81002b42>] system_call_fastpath+0x16/0x1b
    > > >
    > > >
    > > > Shouldn't we drop autofs4_ioctl_mutex while we wait?
    > >
    > > If the ioctl can sleep for multiple seconds, the mutex should
    > > indeed be dropped, and that would be safe because we used to
    > > do the same with the BKL.
    > >
    > > The question is why this would sleep for more than 120 seconds.
    > >
    >
    > Let's fix first and ask questions later.

    You can't hold an exclusive mutex during an autofs expire because the
    daemon will start by calling the ioctl to check for a dentry to expire
    then call back to the daemon to perform the umount and wait for a status
    return (also an ioctl).

    >From memory the expire is the only ioctl that is sensitive to this
    deadlock.

    So, either the mutex must be released while waiting for the status
    return or get rid of the autofs4_ioctl_mutex altogether.

    Ian




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