On Thu, 8 Mar 2012 14:45:16 +0530
"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>
> This fix the below lockdep warning
OK, what's going on here.
> ======================================================
> [ INFO: possible circular locking dependency detected ]
> 3.3.0-rc4+ #190 Not tainted
> -------------------------------------------------------
> shared/1568 is trying to acquire lock:
> (&sb->s_type->i_mutex_key#12){+.+.+.}, at: [<ffffffff811efa0f>] hugetlbfs_file_mmap+0x7d/0x108
>
> but task is already holding lock:
> (&mm->mmap_sem){++++++}, at: [<ffffffff810f5589>] sys_mmap_pgoff+0xd4/0x12f
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&mm->mmap_sem){++++++}:
> [<ffffffff8109fb8f>] lock_acquire+0xd5/0xfa
> [<ffffffff810ee439>] might_fault+0x6d/0x90
> [<ffffffff8111bc12>] filldir+0x6a/0xc2
> [<ffffffff81129942>] dcache_readdir+0x5c/0x222
> [<ffffffff8111be58>] vfs_readdir+0x76/0xac
> [<ffffffff8111bf6a>] sys_getdents+0x79/0xc9
> [<ffffffff816940a2>] system_call_fastpath+0x16/0x1b
>
> -> #0 (&sb->s_type->i_mutex_key#12){+.+.+.}:
> [<ffffffff8109f40a>] __lock_acquire+0xa6c/0xd60
> [<ffffffff8109fb8f>] lock_acquire+0xd5/0xfa
> [<ffffffff816916be>] __mutex_lock_common+0x48/0x350
> [<ffffffff81691a85>] mutex_lock_nested+0x2a/0x31
> [<ffffffff811efa0f>] hugetlbfs_file_mmap+0x7d/0x108
> [<ffffffff810f4fd0>] mmap_region+0x26f/0x466
> [<ffffffff810f545b>] do_mmap_pgoff+0x294/0x2ee
> [<ffffffff810f55a9>] sys_mmap_pgoff+0xf4/0x12f
> [<ffffffff8103d1f2>] sys_mmap+0x1d/0x1f
> [<ffffffff816940a2>] 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#12);
> lock(&mm->mmap_sem);
> lock(&sb->s_type->i_mutex_key#12);
>
> *** DEADLOCK ***
>
> 1 lock held by shared/1568:
> #0: (&mm->mmap_sem){++++++}, at: [<ffffffff810f5589>] sys_mmap_pgoff+0xd4/0x12f
>
> stack backtrace:
> Pid: 1568, comm: shared Not tainted 3.3.0-rc4+ #190
> Call Trace:
> [<ffffffff81688bf9>] print_circular_bug+0x1f8/0x209
> [<ffffffff8109f40a>] __lock_acquire+0xa6c/0xd60
> [<ffffffff8110e7b6>] ? files_lglock_local_lock_cpu+0x61/0x61
> [<ffffffff811efa0f>] ? hugetlbfs_file_mmap+0x7d/0x108
> [<ffffffff8109fb8f>] lock_acquire+0xd5/0xfa
> [<ffffffff811efa0f>] ? hugetlbfs_file_mmap+0x7d/0x108
>
Why have these lockdep warnings started coming out now - was the VFS
changed to newly take i_mutex somewhere in the directory handling?
Sigh. Was lockdep_annotate_inode_mutex_key() sufficiently
self-explanatory to justify leaving it undocumented?
<goes off and reads e096d0c7e2e>
OK, the patch looks correct given the explanation in e096d0c7e2e, but
I'd like to understand why it becomes necessary only now.
> NOTE: This patch also require
> http://thread.gmane.org/gmane.linux.file-systems/58795/focus=59565
> to remove the lockdep warning
And that patch has been basically ignored.
Sigh. I guess I'll grab both patches, but I'm not confident in doing
so without an overall explanation of what is happening here.
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