On Mon, Jan 16, 2012 at 08:45:29PM +0000, Al Viro wrote: > On Mon, Jan 16, 2012 at 09:26:00AM -0500, Josef Bacik wrote: > > On Mon, Jan 16, 2012 at 09:53:23AM +0100, Stanislaw Gruszka wrote: > > > Hi Josef, > > > > > > commit 660d3f6cde552323578b85fc5a09a6742f1fe804 > > > Author: Josef Bacik <jo...@redhat.com> > > > Date: Fri Dec 9 11:18:51 2011 -0500 > > > > > > Btrfs: fix how we do delalloc reservations and how we free > > > reservations on error > > > > > > introduced possible deadlock. According to comment before > > > btrfs_page_mkwrite(), that function is not allowed to take > > > node->i_mutex . > > > > > > The problem was detected by Patrick (full lockdep info is provided): > > > http://bugzilla.kernel.org/attachment.cgi?id=72072 > > > during investigating of some other issue (kernel.org bug 42576) > > > > > > > It's not a deadlock since you can't mmap a directory, but I posted a fix for > > this to linux-btrfs last week, afaik it's headed to -rc1. Thanks, > > Sigh... You know, I'm getting really annoyed with the "can't mmap a > directory" > bogosity resurfacing every couple of months or so. No, you can't mmap a > directory. You also can't bugger a hedgehog, which is about as relevant. > > What you *can* do is write(2) on a regular file. Which will happily grab > ->i_mutex (in case of btrfs, that's done in the beginning of > btrfs_file_aio_write()) and eventually get the user pages in (in case of > btrfs, iov_iter_fault_in_readable() from __btrfs_buffered_write() from > btrfs_file_aio_write()). IOW, you do get pagefaults with ->i_mutex > held. Which means ->mmap_sem grabbed while holding ->i_mutex. No > directories involved...
Good point, either way it's been fixed. Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
