Messages in this thread | | | Date | Fri, 22 Mar 2013 01:40:37 +0000 | From | Al Viro <> | Subject | Re: VFS deadlock ? |
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On Thu, Mar 21, 2013 at 06:33:35PM -0700, Linus Torvalds wrote: > On Thu, Mar 21, 2013 at 6:22 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > > > In theory, we can make vfs_rmdir() and vfs_unlink() check the presense of > > the corresponding method before locking the victim; that would suffice to > > kludge around that mess on procfs. Along with ->d_inode comparison in > > lock_rename() it *might* suffice. > > Hmm, yes. Maybe we can do that as a stopgap, backport that, and leave > any bigger changes for the development tree. That would make the issue > less urgent, never mind all the other worries about backporting > complicated patches for subtle issues. > > I realize you aren't entirely thrilled about it, but we actually > already seem to do that check in both vfs_rmdir().and vfs_unlink() > before getting the child i_mutex. I wonder if that is because we've > already seen lockdep splats for this case...
Yeah, I went to do such patch after sending the previous mail and noticed that we already did it that way. Simplicity of error recovery was probably more important consideration there - I honestly don't remember the reasoning in such details; it had been a decade or so... So lock_rename() doing ->d_inode comparison (with dire comment re not expecting that to be sufficient for anything other than this bug in procfs) will probably suffice for fs/namei.c part of it; I'm still looking at dcache.c side of things...
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