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Subject[PATCH 5/8] xfs: Protect xfs_file_aio_write() & xfs_setattr_size() with sb_start_write - sb_end_write
Date
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.

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.

CC: Ben Myers <bpm@sgi.com>
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);

/* No fallback to buffered IO on errors for XFS. */
ASSERT(ret < 0 || ret == count);
@@ -899,6 +901,7 @@ xfs_file_buffered_aio_write(
/* We can write back this queue in page reclaim */
current->backing_dev_info = mapping->backing_dev_info;

+ sb_start_write(inode->i_sb, SB_FREEZE_WRITE);
write_retry:
trace_xfs_file_buffered_write(ip, count, iocb->ki_pos, 0);
ret = generic_file_buffered_write(iocb, iovp, nr_segs,
@@ -914,6 +917,7 @@ write_retry:
enospc = 1;
goto write_retry;
}
+ sb_end_write(inode->i_sb, SB_FREEZE_WRITE);
current->backing_dev_info = NULL;
return ret;
}
@@ -945,8 +949,6 @@ xfs_file_aio_write(
if (ocount == 0)
return 0;

- xfs_wait_for_freeze(ip->i_mount, SB_FREEZE_WRITE);
-
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);
+
tp = xfs_trans_alloc(mp, XFS_TRANS_SETATTR_SIZE);
error = xfs_trans_reserve(tp, 0, XFS_ITRUNCATE_LOG_RES(mp), 0,
XFS_TRANS_PERM_LOG_RES,
@@ -924,6 +929,7 @@ xfs_setattr_size(

error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
out_unlock:
+ sb_end_write(inode->i_sb, SB_FREEZE_WRITE);
if (lock_flags)
xfs_iunlock(ip, lock_flags);
return error;
--
1.7.1


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