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    SubjectRe: hugetlbfs lockdep spew revisited.
    On 2012-02-16 19:16:34, Josh Boyer wrote:
    > On Thu, Feb 16, 2012 at 07:08:57PM -0500, Dave Jones wrote:
    > > Remember this ? https://lkml.org/lkml/2011/4/15/272
    > > Josh took a stab at fixing it in e096d0c7e2e4e5893792db865dd065ac73cf1f00,
    > > but it seems to still be there.
    >
    > I think Tyler Hicks actually noticed this a while ago, but his patch has
    > been waiting on comment from Al and Christoph:
    >
    > http://thread.gmane.org/gmane.linux.file-systems/58795/focus=59565
    >
    > I've been hesitant to comment because I obviously screwed up once
    > already. We could try this patch in Fedora for a while if Al and
    > company don't speak up soon.

    I'm pretty confident that my patch that Josh linked to would "fix" the
    lockdep warning below. According to the backtrace, it is barking about a
    directory inode and a regular inode having a circular locking
    dependency, so deadlock is not possible in this case.

    akpm picked up my patch in the mm tree, but it still hasn't made it into
    mainline.

    Tyler

    >
    > josh
    >
    > >
    > > Dave
    > >
    > >
    > > ======================================================
    > > [ INFO: possible circular locking dependency detected ]
    > > 3.3.0-rc3+ #2 Not tainted
    > > -------------------------------------------------------
    > > trinity/30663 is trying to acquire lock:
    > > (&sb->s_type->i_mutex_key#18){+.+...}, at: [<ffffffff81298169>] hugetlbfs_file_mmap+0x89/0x140
    > >
    > > but task is already holding lock:
    > > (&mm->mmap_sem){++++++}, at: [<ffffffff81182d97>] sys_mmap_pgoff+0x1d7/0x230
    > >
    > > which lock already depends on the new lock.
    > >
    > >
    > > the existing dependency chain (in reverse order) is:
    > >
    > > -> #1 (&mm->mmap_sem){++++++}:
    > > [<ffffffff810d073d>] lock_acquire+0x9d/0x220
    > > [<ffffffff811789c0>] might_fault+0x80/0xb0
    > > [<ffffffff811d2997>] filldir+0x77/0xe0
    > > [<ffffffff811e61ae>] dcache_readdir+0x5e/0x220
    > > [<ffffffff811d2c68>] vfs_readdir+0xb8/0xf0
    > > [<ffffffff811d2d99>] sys_getdents+0x89/0x100
    > > [<ffffffff816a5b69>] system_call_fastpath+0x16/0x1b
    > >
    > > -> #0 (&sb->s_type->i_mutex_key#18){+.+...}:
    > > [<ffffffff810d0008>] __lock_acquire+0x1bf8/0x1c20
    > > [<ffffffff810d073d>] lock_acquire+0x9d/0x220
    > > [<ffffffff8169a5b9>] __mutex_lock_common+0x59/0x500
    > > [<ffffffff8169ab94>] mutex_lock_nested+0x44/0x50
    > > [<ffffffff81298169>] hugetlbfs_file_mmap+0x89/0x140
    > > [<ffffffff811826a9>] mmap_region+0x369/0x4f0
    > > [<ffffffff81182b9f>] do_mmap_pgoff+0x36f/0x390
    > > [<ffffffff81182db7>] sys_mmap_pgoff+0x1f7/0x230
    > > [<ffffffff8101eda2>] sys_mmap+0x22/0x30
    > > [<ffffffff816a5b69>] system_call_fastpath+0x16/0x1b
    > >
    > > other info that might help us debug this:
    > >
    > > Possible unsafe locking scenario:
    > >
    > > CPU0 CPU1
    > > ---- ----
    > > lock(&mm->mmap_sem);
    > > lock(&sb->s_type->i_mutex_key#18);
    > > lock(&mm->mmap_sem);
    > > lock(&sb->s_type->i_mutex_key#18);
    > >
    > > *** DEADLOCK ***
    > >
    > > 1 lock held by trinity/30663:
    > > #0: (&mm->mmap_sem){++++++}, at: [<ffffffff81182d97>] sys_mmap_pgoff+0x1d7/0x230
    > >
    > > stack backtrace:
    > > Pid: 30663, comm: trinity Not tainted 3.3.0-rc3+ #2
    > > Call Trace:
    > > [<ffffffff816924d7>] print_circular_bug+0x1fb/0x20c
    > > [<ffffffff810d0008>] __lock_acquire+0x1bf8/0x1c20
    > > [<ffffffff816a1c2d>] ? sub_preempt_count+0x9d/0xd0
    > > [<ffffffff811a40cc>] ? deactivate_slab+0x54c/0x5f0
    > > [<ffffffff810d073d>] lock_acquire+0x9d/0x220
    > > [<ffffffff81298169>] ? hugetlbfs_file_mmap+0x89/0x140
    > > [<ffffffff810d12fd>] ? trace_hardirqs_on_caller+0x10d/0x1a0
    > > [<ffffffff8169a5b9>] __mutex_lock_common+0x59/0x500
    > > [<ffffffff81298169>] ? hugetlbfs_file_mmap+0x89/0x140
    > > [<ffffffff811825e5>] ? mmap_region+0x2a5/0x4f0
    > > [<ffffffff81298169>] ? hugetlbfs_file_mmap+0x89/0x140
    > > [<ffffffff8169ab94>] mutex_lock_nested+0x44/0x50
    > > [<ffffffff81298169>] hugetlbfs_file_mmap+0x89/0x140
    > > [<ffffffff811826a9>] mmap_region+0x369/0x4f0
    > > [<ffffffff812c1e9a>] ? file_map_prot_check+0xaa/0xe0
    > > [<ffffffff81182b9f>] do_mmap_pgoff+0x36f/0x390
    > > [<ffffffff81182d97>] ? sys_mmap_pgoff+0x1d7/0x230
    > > [<ffffffff81182db7>] sys_mmap_pgoff+0x1f7/0x230
    > > [<ffffffff810d12fd>] ? trace_hardirqs_on_caller+0x10d/0x1a0
    > > [<ffffffff8101eda2>] sys_mmap+0x22/0x30
    > > [<ffffffff816a5b69>] system_call_fastpath+0x16/0x1b
    > >
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