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Commit c58cb165 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Alex Elder
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xfs: avoid direct I/O write vs buffered I/O race 



Currently a buffered reader or writer can add pages to the pagecache
while we are waiting for the iolock in xfs_file_dio_aio_write.  Prevent
this by re-checking mapping->nrpages after we got the iolock, and if
nessecary upgrade the lock to exclusive mode.  To simplify this a bit
only take the ilock inside of xfs_file_aio_write_checks.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
Signed-off-by: default avatarAlex Elder <aelder@sgi.com>
parent 859f57ca

fs/xfs/xfs_file.c

+14 −3
Original line number Diff line number Diff line
@@ -676,6 +676,7 @@ xfs_file_aio_write_checks( 
	xfs_fsize_t		new_size;

	int			error = 0;



	xfs_rw_ilock(ip, XFS_ILOCK_EXCL);

	*new_sizep = 0;

restart:

	error = generic_write_checks(file, pos, count, S_ISBLK(inode->i_mode));
@@ -798,14 +799,24 @@ xfs_file_dio_aio_write( 
		*iolock = XFS_IOLOCK_EXCL;

	else

		*iolock = XFS_IOLOCK_SHARED;

	xfs_rw_ilock(ip, XFS_ILOCK_EXCL | *iolock);

	xfs_rw_ilock(ip, *iolock);



	/*

	 * Recheck if there are cached pages that need invalidate after we got

	 * the iolock to protect against other threads adding new pages while

	 * we were waiting for the iolock.

	 */

	if (mapping->nrpages && *iolock == XFS_IOLOCK_SHARED) {

		xfs_rw_iunlock(ip, *iolock);

		*iolock = XFS_IOLOCK_EXCL;

		xfs_rw_ilock(ip, *iolock);

	}



	ret = xfs_file_aio_write_checks(file, &pos, &count, new_size, iolock);

	if (ret)

		return ret;



	if (mapping->nrpages) {

		WARN_ON(*iolock != XFS_IOLOCK_EXCL);

		ret = -xfs_flushinval_pages(ip, (pos & PAGE_CACHE_MASK), -1,

							FI_REMAPF_LOCKED);

		if (ret)
@@ -851,7 +862,7 @@ xfs_file_buffered_aio_write( 
	size_t			count = ocount;



	*iolock = XFS_IOLOCK_EXCL;

	xfs_rw_ilock(ip, XFS_ILOCK_EXCL | *iolock);

	xfs_rw_ilock(ip, *iolock);



	ret = xfs_file_aio_write_checks(file, &pos, &count, new_size, iolock);

	if (ret)