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: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Dave Chinner 2018-06-07 07:46:42 -07:00 committed by Darrick J. Wong
parent ef215e394e
commit 4a2d01b076
3 changed files with 12 additions and 1 deletions

View File

@ -531,8 +531,19 @@ xfs_submit_ioend(
{
/* Convert CoW extents to regular */
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),
ioend->io_offset, ioend->io_size);
memalloc_nofs_restore(nofs_flag);
}
/* Reserve log space if we might write beyond the on-disk inode size. */

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@ -21,7 +21,6 @@
#include <linux/migrate.h>
#include <linux/backing-dev.h>
#include <linux/freezer.h>
#include <linux/sched/mm.h>
#include "xfs_format.h"
#include "xfs_log_format.h"

View File

@ -26,6 +26,7 @@ typedef __u32 xfs_nlink_t;
#include <linux/semaphore.h>
#include <linux/mm.h>
#include <linux/sched/mm.h>
#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/slab.h>