Re: hugetlbfs lockdep spew revisited.

[Tyler Hicks <tyhicks@canonical.com>]

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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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