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NFS: swap-out must always use STABLE writes.

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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@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
This commit is contained in:
NeilBrown 2022-03-07 10:41:44 +11:00 committed by Trond Myklebust
parent 64158668ac
commit c265de257f
1 changed files with 6 additions and 4 deletions
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10
fs/nfs/direct.c
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@ -794,7 +794,7 @@ 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;
@ -802,7 +802,7 @@ 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);
@ -948,11 +948,13 @@ 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,