On Mon, Sep 24, 2007 at 06:07:38PM -0400, Trond Myklebust wrote: > I'm seeing lockdep warning about a potential lock inversion between > &mm->mmap_sem and &inode->i_mutex in NFS (see attachment). > > Unfortunately the basis for the warning appears to be the behaviour in > ext3(???). AFAICS there is no way for NFS to share an inode->i_mutex > with ext3. What to do?
Actually this can probably happen just on NFS alone. > > Trond > ======================================================= > [ INFO: possible circular locking dependency detected ] > 2.6.23-rc7-g8809e921 #1 > ------------------------------------------------------- > beagle-build-in/24375 is trying to acquire lock: > (&mm->mmap_sem){----}, at: [<c05a2887>] do_page_fault+0x17d/0x591 > > but task is already holding lock: > (&inode->i_mutex){--..}, at: [<c059f9e3>] mutex_lock+0x1c/0x1f > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #1 (&inode->i_mutex){--..}: > [<c043d4da>] __lock_acquire+0x9f3/0xba6 > [<c043da62>] lock_acquire+0x5f/0x78 > [<c059f832>] __mutex_lock_slowpath+0xe5/0x27a > [<c059f9e3>] mutex_lock+0x1c/0x1f > [<f8c92495>] nfs_revalidate_mapping+0x64/0x9c [nfs] > [<f8c8ff2a>] nfs_file_mmap+0x46/0x75 [nfs] > [<c046097c>] mmap_region+0x1ea/0x3b8 > [<c0460e9b>] do_mmap_pgoff+0x27b/0x2da > [<c0407d77>] sys_mmap2+0x9b/0xb5 > [<c040405e>] sysenter_past_esp+0x5f/0x99 > [<ffffffff>] 0xffffffff > > -> #0 (&mm->mmap_sem){----}: > [<c043d3c6>] __lock_acquire+0x8df/0xba6 > [<c043da62>] lock_acquire+0x5f/0x78 > [<c04360db>] down_read+0x3a/0x4c > [<c05a2887>] do_page_fault+0x17d/0x591 > [<c05a1382>] error_code+0x72/0x78 > [<f88acaac>] call_filldir+0xac/0xc3 [ext3] > [<f88acdb2>] ext3_readdir+0x217/0x5e5 [ext3] > [<c04798a1>] vfs_readdir+0x67/0x93 > [<c0479af6>] sys_getdents+0x5f/0x9d > [<c040405e>] sysenter_past_esp+0x5f/0x99 > [<ffffffff>] 0xffffffff The circular lock seems to be this: #1: sys_mmap2: down_write(&mm->mmap_sem); nfs_revalidate_mapping: mutex_lock(&inode->i_mutex); #0: vfs_readdir: mutex_lock(&inode->i_mutex); - during the readdir (filldir64), we take a user fault (missing page?) and call do_page_fault - do_page_fault: down_read(&mm->mmap_sem); So it does indeed look like a circular locking. Now the question is, "is this a bug?". Looking like the inode of #1 must be a file or something else that you can mmap and the inode of #0 seems it must be a directory. I would say "no". Now if you can readdir on a file or mmap a directory, then this could be an issue. Otherwise, I'd love to see someone teach lockdep about this issue! ;-) -- Steve - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/