Hi Josef,
commit 660d3f6cde552323578b85fc5a09a6742f1fe804
Author: Josef Bacik <josef@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)
Stanislaw
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On Mon, Jan 16, 2012 at 09:53:23AM +0100, Stanislaw Gruszka wrote:> Hi Josef, > > commit 660d3f6cde552323578b85fc5a09a6742f1fe804 > Author: Josef Bacik <josef@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, Joesf -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 <josef@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... -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 <josef@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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 17/01/12 09:01, Josef Bacik wrote:> Good point, either way it''s been fixed. Thanks,Is it worth pushing that fix into the stable 3.2.x releases ? cheers, Chris -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html