The commit handling code is not safe against memory-pressure deadlocks
when writing to swap. In particular, nfs_commitdata_alloc() blocks
indefinitely waiting for memory, and this can consume all available
workqueue threads.
swap-out most likely uses STABLE writes anyway as COND_STABLE indicates
that a stable write should be used if the write fits in a single
request, and it normally does. However if we ever swap with a small
wsize, or gather unusually large numbers of pages for a single write,
this might change.
For safety, make it explicit in the code that direct writes used for swap
must always use FLUSH_STABLE.
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
fs/nfs/direct.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index c5c53219beeb..4eb2a8380a28 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -791,7 +791,7 @@ static const struct nfs_pgio_completion_ops nfs_direct_write_completion_ops = {
*/
static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
struct iov_iter *iter,
- loff_t pos)
+ loff_t pos, int ioflags)
{
struct nfs_pageio_descriptor desc;
struct inode *inode = dreq->inode;
@@ -799,7 +799,7 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
size_t requested_bytes = 0;
size_t wsize = max_t(size_t, NFS_SERVER(inode)->wsize, PAGE_SIZE);
- nfs_pageio_init_write(&desc, inode, FLUSH_COND_STABLE, false,
+ nfs_pageio_init_write(&desc, inode, ioflags, false,
&nfs_direct_write_completion_ops);
desc.pg_dreq = dreq;
get_dreq(dreq);
@@ -945,11 +945,13 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter,
pnfs_init_ds_commit_info_ops(&dreq->ds_cinfo, inode);
if (swap) {
- requested = nfs_direct_write_schedule_iovec(dreq, iter, pos);
+ requested = nfs_direct_write_schedule_iovec(dreq, iter, pos,
+ FLUSH_STABLE);
} else {
nfs_start_io_direct(inode);
- requested = nfs_direct_write_schedule_iovec(dreq, iter, pos);
+ requested = nfs_direct_write_schedule_iovec(dreq, iter, pos,
+ FLUSH_COND_STABLE);
if (mapping->nrpages) {
invalidate_inode_pages2_range(mapping,
