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    SubjectRe: .29rc2 lockdep report. fb_mmap vs sys_mmap2
    On 2009-01-18 03:00, Johannes Weiner wrote:
    > On Sat, Jan 17, 2009 at 06:19:25PM -0500, Dave Jones wrote:
    >> Two mmaps enter! Fight!
    >>
    >>
    >> =======================================================
    >> [ INFO: possible circular locking dependency detected ]
    >> 2.6.29-0.41.rc2.fc11.i686 #1
    >> -------------------------------------------------------
    >> plymouthd/669 is trying to acquire lock:
    >> (&fb_info->lock){--..}, at: [<c055355c>] fb_mmap+0x87/0x156
    >>
    >> but task is already holding lock:
    >> (&mm->mmap_sem){----}, at: [<c0406a5d>] sys_mmap2+0x44/0x7b
    >>
    >> which lock already depends on the new lock.
    >>
    >>
    >> the existing dependency chain (in reverse order) is:
    >>
    >> -> #1 (&mm->mmap_sem){----}:
    >> [<c044fef3>] __lock_acquire+0x9af/0xb22
    >> [<c04500c1>] lock_acquire+0x5b/0x81
    >> [<c048e036>] might_fault+0x60/0x80
    >> [<c053dedc>] copy_to_user+0x2c/0xfc
    >> [<c05542cc>] fb_ioctl+0x247/0x338
    >> [<c04b0c9f>] vfs_ioctl+0x22/0x69
    >> [<c04b1214>] do_vfs_ioctl+0x46a/0x4a3
    >> [<c04b128d>] sys_ioctl+0x40/0x5a
    >> [<c0403b76>] syscall_call+0x7/0xb
    >> [<ffffffff>] 0xffffffff
    >>
    >> -> #0 (&fb_info->lock){--..}:
    >> [<c044fdc8>] __lock_acquire+0x884/0xb22
    >> [<c04500c1>] lock_acquire+0x5b/0x81
    >> [<c06e1b98>] __mutex_lock_common+0xd5/0x329
    >> [<c06e1e84>] mutex_lock_nested+0x2e/0x36
    >> [<c055355c>] fb_mmap+0x87/0x156
    >> [<c0494620>] mmap_region+0x22b/0x43c
    >> [<c0494aa2>] do_mmap_pgoff+0x271/0x2d1
    >> [<c0406a73>] sys_mmap2+0x5a/0x7b
    >> [<c0403b76>] syscall_call+0x7/0xb
    >> [<ffffffff>] 0xffffffff
    >>
    >> other info that might help us debug this:
    >>
    >> 1 lock held by plymouthd/669:
    >> #0: (&mm->mmap_sem){----}, at: [<c0406a5d>] sys_mmap2+0x44/0x7b
    >>
    >> stack backtrace:
    >> Pid: 669, comm: plymouthd Not tainted 2.6.29-0.41.rc2.fc11.i686 #1
    >> Call Trace:
    >> [<c06e09b6>] ? printk+0xf/0x11
    >> [<c044f32d>] print_circular_bug_tail+0x5d/0x68
    >> [<c044fdc8>] __lock_acquire+0x884/0xb22
    >> [<c04500c1>] lock_acquire+0x5b/0x81
    >> [<c055355c>] ? fb_mmap+0x87/0x156
    >> [<c06e1b98>] __mutex_lock_common+0xd5/0x329
    >> [<c055355c>] ? fb_mmap+0x87/0x156
    >> [<c06e1e84>] mutex_lock_nested+0x2e/0x36
    >> [<c055355c>] ? fb_mmap+0x87/0x156
    >> [<c055355c>] fb_mmap+0x87/0x156
    >> [<c0494620>] mmap_region+0x22b/0x43c
    >> [<c0494aa2>] do_mmap_pgoff+0x271/0x2d1
    >> [<c0406a73>] sys_mmap2+0x5a/0x7b
    >> [<c0403b76>] syscall_call+0x7/0xb
    >
    > I reported this one already some time ago [1], Andrea Righi [cc'd]
    > also had a fix [2] but it seemed to not have made it in. Andrea,
    > perhaps you can resend it?
    >
    > Hannes
    >
    > [1] http://lkml.org/lkml/2008/10/22/759
    > [2] http://lkml.org/lkml/2008/10/28/377

    Sure, I can resend it soon, after a test.

    -Andrea


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