On Thu, Jun 27, 2019 at 03:30:30PM -0700, Darrick J. Wong wrote:
> I think the wording of this is too indirect. The reason we need to set
> NOFS is because we could be doing writeback as part of reclaiming
> memory, which means that we cannot recurse back into filesystems to
> satisfy the memory allocation needed to create a transaction. The NOFS
> part applies to any memory allocation, of course.
>
> If you're fine with the wording below I'll just edit that into the
> patch:
>
> /*
> * We can allocate memory here while doing writeback on behalf of
> * memory reclaim. To avoid memory allocation deadlocks set the
> * task-wide nofs context for the following operations.
> */
> nofs_flag = memalloc_nofs_save();
Fine with me.
> > trace_xfs_end_io_direct_write(ip, offset, size);
> > @@ -395,10 +396,11 @@ xfs_dio_write_end_io(
> > */
> > XFS_STATS_ADD(ip->i_mount, xs_write_bytes, size);
> >
> > + nofs_flag = memalloc_nofs_save();
>
> Hmm, do we need this here? I can't remember if there was a need for
> setting NOFS under xfs_reflink_end_cow from a dio completion or if that
> was purely the buffered writeback case...
We certainly had to add it for the unwritten extent conversion, maybe
the corner case just didn't manage to show up for COW yet:
commit 80641dc66a2d6dfb22af4413227a92b8ab84c7bb
Author: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Mon Oct 19 04:00:03 2009 +0000
xfs: I/O completion handlers must use NOFS allocations
When completing I/O requests we must not allow the memory allocator to
recurse into the filesystem, as we might deadlock on waiting for the
I/O completion otherwise. The only thing currently allocating normal
GFP_KERNEL memory is the allocation of the transaction structure for
the unwritten extent conversion. Add a memflags argument to
_xfs_trans_alloc to allow controlling the allocator behaviour.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reported-by: Thomas Neumann <tneumann@xxxxxxxxxxxxxxxxxxxxx>
Tested-by: Thomas Neumann <tneumann@xxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Alex Elder <aelder@xxxxxxx>
Signed-off-by: Alex Elder <aelder@xxxxxxx>
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 2d0b3e1da9e6..6f83f58c099f 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -611,7 +611,7 @@ xfs_fs_log_dummy(
xfs_inode_t *ip;
int error;
- tp = _xfs_trans_alloc(mp, XFS_TRANS_DUMMY1);
+ tp = _xfs_trans_alloc(mp, XFS_TRANS_DUMMY1, KM_SLEEP);
error = xfs_trans_reserve(tp, 0, XFS_ICHANGE_LOG_RES(mp), 0, 0, 0);
if (error) {
xfs_trans_cancel(tp, 0);
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 67ae5555a30a..7294abce6ef2 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -860,8 +860,15 @@ xfs_iomap_write_unwritten(
* set up a transaction to convert the range of extents
* from unwritten to real. Do allocations in a loop until
* we have covered the range passed in.
+ *
+ * Note that we open code the transaction allocation here
+ * to pass KM_NOFS--we can't risk to recursing back into
+ * the filesystem here as we might be asked to write out
+ * the same inode that we complete here and might deadlock
+ * on the iolock.
*/
- tp = xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE);
+ xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
+ tp = _xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE, KM_NOFS);
tp->t_flags |= XFS_TRANS_RESERVE;
error = xfs_trans_reserve(tp, resblks,
XFS_WRITE_LOG_RES(mp), 0,
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 8b6c9e807efb..4d509f742bd2 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1471,7 +1471,7 @@ xfs_log_sbcount(
if (!xfs_sb_version_haslazysbcount(&mp->m_sb))
return 0;
- tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT);
+ tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP);
error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
XFS_DEFAULT_LOG_COUNT);
if (error) {
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 66b849358e62..237badcbac3b 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -236,19 +236,20 @@ xfs_trans_alloc(
uint type)
{
xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
- return _xfs_trans_alloc(mp, type);
+ return _xfs_trans_alloc(mp, type, KM_SLEEP);
}
xfs_trans_t *
_xfs_trans_alloc(
xfs_mount_t *mp,
- uint type)
+ uint type,
+ uint memflags)
{
xfs_trans_t *tp;
atomic_inc(&mp->m_active_trans);
- tp = kmem_zone_zalloc(xfs_trans_zone, KM_SLEEP);
+ tp = kmem_zone_zalloc(xfs_trans_zone, memflags);
tp->t_magic = XFS_TRANS_MAGIC;
tp->t_type = type;
tp->t_mountp = mp;
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index ed47fc77759c..a0574f593f52 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -924,7 +924,7 @@ typedef struct xfs_trans {
* XFS transaction mechanism exported interfaces.
*/
xfs_trans_t *xfs_trans_alloc(struct xfs_mount *, uint);
-xfs_trans_t *_xfs_trans_alloc(struct xfs_mount *, uint);
+xfs_trans_t *_xfs_trans_alloc(struct xfs_mount *, uint, uint);
xfs_trans_t *xfs_trans_dup(xfs_trans_t *);
int xfs_trans_reserve(xfs_trans_t *, uint, uint, uint,
uint, uint);
