On Thu, Jun 07, 2018 at 07:41:40AM -0400, Brian Foster wrote:
> On Thu, Jun 07, 2018 at 03:21:32PM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
>
> Looks fine modulo the header thing Allison already pointed out:
>
> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
>
> BTW, shouldn't we also be using XFS_TRANS_NOFS in
> xfs_iomap_write_allocate()?
/me squints at the usage and thinks ... yes probably. :)
--D
> Brian
>
> > fs/xfs/xfs_aops.c | 11 +++++++++++
> > fs/xfs/xfs_buf.c | 1 -
> > fs/xfs/xfs_linux.h | 1 +
> > 3 files changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> > index 767d53222f31..1eb625fdcb1e 100644
> > --- a/fs/xfs/xfs_aops.c
> > +++ b/fs/xfs/xfs_aops.c
> > @@ -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. */
> > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> > index 980bc48979e9..e9c058e3761c 100644
> > --- a/fs/xfs/xfs_buf.c
> > +++ b/fs/xfs/xfs_buf.c
> > @@ -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"
> > diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
> > index ae1e66fa3f61..1631cf4546f2 100644
> > --- a/fs/xfs/xfs_linux.h
> > +++ b/fs/xfs/xfs_linux.h
> > @@ -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>
> > --
> > 2.17.0
> >
> > --
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