Re: [PATCH 5/8] xfs: Protect xfs_file_aio_write() & xfs_setattr_size() with sb_start_write - sb_end_write
From: Dave Chinner <david@fromorbit.com>
Date: 2012-01-24 07:19:26
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linux-ext4, linux-fsdevel, lkml
On Fri, Jan 20, 2012 at 09:34:43PM +0100, Jan Kara wrote:
Replace racy xfs_wait_for_freeze() check in xfs_file_aio_write() with a reliable sb_start_write() - sb_end_write() locking. Due to lock ranking dictated by the page fault code we have to call sb_start_write() after we acquire ilock.
It appears to me that you have indeed confused the ilock with the iolock.
Similarly we have to protect xfs_setattr_size() because it can modify last page of truncated file. Because ilock is dropped in xfs_setattr_size() we have to drop and retake write access as well to avoid deadlocks.
quoted hunk ↗ jump to hunk
CC: Ben Myers <redacted> CC: Alex Elder <elder@kernel.org> Signed-off-by: Jan Kara <jack@suse.cz> --- fs/xfs/xfs_file.c | 6 ++++-- fs/xfs/xfs_iops.c | 6 ++++++ 2 files changed, 10 insertions(+), 2 deletions(-)diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 753ed9b..9efd153 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c@@ -862,9 +862,11 @@ xfs_file_dio_aio_write( *iolock = XFS_IOLOCK_SHARED; } + sb_start_write(inode->i_sb, SB_FREEZE_WRITE); trace_xfs_file_direct_write(ip, count, iocb->ki_pos, 0); ret = generic_file_direct_write(iocb, iovp, &nr_segs, pos, &iocb->ki_pos, count, ocount); + sb_end_write(inode->i_sb, SB_FREEZE_WRITE);
That's inside the iolock, not the ilock. Either way, it is incorrect. This accounting should be outside the iolock - because xfs_trans_alloc() can be called with the iolock held. Therefore the freeze/lock order needs to be sb_start_write(SB_FREEZE_WRITE) XFS(ip)->i_iolock XFS(ip)->i_ilock sb_end_write(SB_FREEZE_WRITE) Which matches the current freeze/lock order.
quoted hunk ↗ jump to hunk
@@ -945,8 +949,6 @@ xfs_file_aio_write( if (ocount == 0) return 0; - xfs_wait_for_freeze(ip->i_mount, SB_FREEZE_WRITE); -
that's where sb_start_write() needs to be, and the sb-end_write() call needs to below the generic_write_sync() calls that will trigger IO on O_SYNC writes. Otherwise it is not covering all the IO path correctly.
quoted hunk ↗ jump to hunk
if (XFS_FORCED_SHUTDOWN(ip->i_mount)) return -EIO;diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c index 3579bc8..798b9c6 100644 --- a/fs/xfs/xfs_iops.c +++ b/fs/xfs/xfs_iops.c@@ -793,6 +793,7 @@ xfs_setattr_size( return xfs_setattr_nonsize(ip, iattr, 0); } + sb_start_write(inode->i_sb, SB_FREEZE_WRITE); /* * Make sure that the dquots are attached to the inode. */@@ -849,10 +850,14 @@ xfs_setattr_size( xfs_get_blocks); if (error) goto out_unlock; + /* Drop the write access to avoid lock inversion with ilock */ + sb_end_write(inode->i_sb, SB_FREEZE_WRITE); xfs_ilock(ip, XFS_ILOCK_EXCL); lock_flags |= XFS_ILOCK_EXCL; + sb_start_write(inode->i_sb, SB_FREEZE_WRITE); +
This is caused by the previous problems I pointed out. You should not need to drop the freeze reference here at all. Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs