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Commit 4a2d01b0 authored by Dave Chinner's avatar Dave Chinner Committed by Darrick J. Wong
Browse files

xfs: xfs_reflink_convert_cow() memory allocation deadlock 



xfs_reflink_convert_cow() manipulates the incore extent list
in GFP_KERNEL context in the IO submission path whilst holding
locked pages under writeback. This is a memory reclaim deadlock
vector. This code is not in a transaction, so any memory allocations
it makes aren't protected via the memalloc_nofs_save() context that
transactions carry.

Hence we need to run this call under memalloc_nofs_save() context to
prevent potential memory allocations from being run as GFP_KERNEL
and deadlocking.

Signed-Off-By: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarAllison Henderson <allison.henderson@oracle.com>
Reviewed-by: default avatarBrian Foster <bfoster@redhat.com>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent ef215e39

fs/xfs/xfs_aops.c

+11 −0
Original line number Original line Diff line number Diff line
@@ -531,8 +531,19 @@ xfs_submit_ioend( 
{

{

	/* Convert CoW extents to regular */

	/* Convert CoW extents to regular */

	if (!status && ioend->io_type == XFS_IO_COW) {

	if (!status && ioend->io_type == XFS_IO_COW) {

		/*

		 * Yuk. This can do memory allocation, but is not a

		 * transactional operation so everything is done in GFP_KERNEL

		 * context. That can deadlock, because we hold pages in

		 * writeback state and GFP_KERNEL allocations can block on them.

		 * Hence we must operate in nofs conditions here.

		 */

		unsigned nofs_flag;



		nofs_flag = memalloc_nofs_save();

		status = xfs_reflink_convert_cow(XFS_I(ioend->io_inode),

		status = xfs_reflink_convert_cow(XFS_I(ioend->io_inode),

				ioend->io_offset, ioend->io_size);

				ioend->io_offset, ioend->io_size);

		memalloc_nofs_restore(nofs_flag);

	}

	}





	/* Reserve log space if we might write beyond the on-disk inode size. */

	/* Reserve log space if we might write beyond the on-disk inode size. */

fs/xfs/xfs_buf.c

+0 −1
Original line number Original line Diff line number Diff line
@@ -21,7 +21,6 @@ 
#include <linux/migrate.h>

#include <linux/migrate.h>

#include <linux/backing-dev.h>

#include <linux/backing-dev.h>

#include <linux/freezer.h>

#include <linux/freezer.h>

#include <linux/sched/mm.h>





#include "xfs_format.h"

#include "xfs_format.h"

#include "xfs_log_format.h"

#include "xfs_log_format.h"

fs/xfs/xfs_linux.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -26,6 +26,7 @@ typedef __u32 xfs_nlink_t; 




#include <linux/semaphore.h>

#include <linux/semaphore.h>

#include <linux/mm.h>

#include <linux/mm.h>

#include <linux/sched/mm.h>

#include <linux/kernel.h>

#include <linux/kernel.h>

#include <linux/blkdev.h>

#include <linux/blkdev.h>

#include <linux/slab.h>

#include <linux/slab.h>