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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 15 Apr 2011 13:49:04 -0700
Message-ID: <BANLkTi=ctr7tQLArfbdHRU3uUvEPh6KbwQ@mail.gmail.com>
Subject: Re: hugetlb locking bug.
To: Dave Jones <davej@redhat.com>, Linux Kernel <linux-kernel@vger.kernel.org>,
        William Irwin <wli@holomorphy.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>
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Hmm. Adding the hugetlbfs/lockdep people to the cc.

This _looks_ like the same kind of false positive we've had with some
other cases: we're taking the i_mutex lock only dor directory inodes
(for the readdir) and we take the i_mmap lock only for non-directory
inodes, so you can't actually get any real circular locking issues.

So yes, we do mix the order of i_mmap_sem and i_mutex, but it's
conceptually two "different" kinds of i_mutex that just happen to
share a name.

And I really thought we annotated it as such with different
"lockdep_set_class()" cases (ie the whole

  lockdep_set_class(&inode->i_mutex,&type->i_mutex_dir_key);

for the S_ISDIR case in unlock_new_inode().

Can somebody more alert than me see why this lockdep issue still
triggers with hugetlbfs?

                         Linus

On Fri, Apr 15, 2011 at 1:16 PM, Dave Jones <davej@redhat.com> wrote:
> Just hit this lockdep report..
>
> ? ? ? ?Dave
>
> ?=======================================================
> ?[ INFO: possible circular locking dependency detected ]
> ?2.6.39-rc3+ #3
> ?-------------------------------------------------------
> ?trinity/11299 is trying to acquire lock:
> ?(&sb->s_type->i_mutex_key#18){+.+.+.}, at: [<ffffffff811ebfec>] hugetlbfs_file_mmap+0x7f/0x10d
>
> ?but task is already holding lock:
> ?(&mm->mmap_sem){++++++}, at: [<ffffffff81109097>] sys_mmap_pgoff+0xf8/0x16a
>
> ?which lock already depends on the new lock.
>
>
> ?the existing dependency chain (in reverse order) is:
>
> ?-> #1 (&mm->mmap_sem){++++++}:
> ? ? ? ?[<ffffffff81086c59>] lock_acquire+0xd0/0xfb
> ? ? ? ?[<ffffffff81100cd0>] might_fault+0x89/0xac
> ? ? ? ?[<ffffffff8114159b>] filldir+0x6f/0xc7
> ? ? ? ?[<ffffffff81150075>] dcache_readdir+0x67/0x204
> ? ? ? ?[<ffffffff811417ed>] vfs_readdir+0x78/0xb1
> ? ? ? ?[<ffffffff8114190c>] sys_getdents+0x7e/0xd1
> ? ? ? ?[<ffffffff814c22c2>] system_call_fastpath+0x16/0x1b
>
> ?-> #0 (&sb->s_type->i_mutex_key#18){+.+.+.}:
> ? ? ? ?[<ffffffff810864e6>] __lock_acquire+0x99e/0xc81
> ? ? ? ?[<ffffffff81086c59>] lock_acquire+0xd0/0xfb
> ? ? ? ?[<ffffffff814b9d00>] __mutex_lock_common+0x4c/0x35b
> ? ? ? ?[<ffffffff814ba0d3>] mutex_lock_nested+0x3e/0x43
> ? ? ? ?[<ffffffff811ebfec>] hugetlbfs_file_mmap+0x7f/0x10d
> ? ? ? ?[<ffffffff81108ac8>] mmap_region+0x26d/0x446
> ? ? ? ?[<ffffffff81108f45>] do_mmap_pgoff+0x2a4/0x2fe
> ? ? ? ?[<ffffffff811090b7>] sys_mmap_pgoff+0x118/0x16a
> ? ? ? ?[<ffffffff8100c56c>] sys_mmap+0x22/0x24
> ? ? ? ?[<ffffffff814c22c2>] system_call_fastpath+0x16/0x1b
>
> ?other info that might help us debug this:
>
> ?1 lock held by trinity/11299:
> ?#0: ?(&mm->mmap_sem){++++++}, at: [<ffffffff81109097>] sys_mmap_pgoff+0xf8/0x16a
>
> ?stack backtrace:
> ?Pid: 11299, comm: trinity Not tainted 2.6.39-rc3+ #3
> ?Call Trace:
> ?[<ffffffff814b1126>] print_circular_bug+0xa6/0xb5
> ?[<ffffffff810864e6>] __lock_acquire+0x99e/0xc81
> ?[<ffffffff811ebfec>] ? hugetlbfs_file_mmap+0x7f/0x10d
> ?[<ffffffff81086c59>] lock_acquire+0xd0/0xfb
> ?[<ffffffff811ebfec>] ? hugetlbfs_file_mmap+0x7f/0x10d
> ?[<ffffffff811ebfec>] ? hugetlbfs_file_mmap+0x7f/0x10d
> ?[<ffffffff814b9d00>] __mutex_lock_common+0x4c/0x35b
> ?[<ffffffff811ebfec>] ? hugetlbfs_file_mmap+0x7f/0x10d
> ?[<ffffffff814b3ee2>] ? __slab_alloc+0xdb/0x3b7
> ?[<ffffffff81087043>] ? trace_hardirqs_on_caller+0x10b/0x12f
> ?[<ffffffff814b3eeb>] ? __slab_alloc+0xe4/0x3b7
> ?[<ffffffff81108a12>] ? mmap_region+0x1b7/0x446
> ?[<ffffffff814ba0d3>] mutex_lock_nested+0x3e/0x43
> ?[<ffffffff811ebfec>] hugetlbfs_file_mmap+0x7f/0x10d
> ?[<ffffffff81108ac8>] mmap_region+0x26d/0x446
> ?[<ffffffff81108f45>] do_mmap_pgoff+0x2a4/0x2fe
> ?[<ffffffff811090b7>] sys_mmap_pgoff+0x118/0x16a
> ?[<ffffffff81087043>] ? trace_hardirqs_on_caller+0x10b/0x12f
> ?[<ffffffff8100c56c>] sys_mmap+0x22/0x24
> ?[<ffffffff814c22c2>] system_call_fastpath+0x16/0x1b
>
>
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