Patch "nfs/pnfs: fix nfs_direct_req ref leak when i/o falls back to the mds" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

nfs/pnfs: fix nfs_direct_req ref leak when i/o falls back to the mds

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
nfs-pnfs-fix-nfs_direct_req-ref-leak-when-i-o-falls-back-to-the-mds.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Scott Mayhew <[email protected]>
Date: Fri, 15 Dec 2017 16:12:32 -0500
Subject: nfs/pnfs: fix nfs_direct_req ref leak when i/o falls back to the mds

From: Scott Mayhew <[email protected]>

commit ba4a76f703ab7eb72941fdaac848502073d6e9ee upstream.

Currently when falling back to doing I/O through the MDS (via pnfs_{read|write}_through_mds), the client frees the nfs_pgio_header without releasing the reference taken on the dreq
via pnfs_generic_pg_{read|write}pages -> nfs_pgheader_init -> nfs_direct_pgio_init. It then takes another reference on the dreq via nfs_generic_pg_pgios -> nfs_pgheader_init -> nfs_direct_pgio_init and as a result the requester will become stuck in inode_dio_wait. Once that happens, other processes accessing the inode will become stuck as well.

Ensure that pnfs_read_through_mds() and pnfs_write_through_mds() clean up correctly by calling hdr->completion_ops->completion() instead of calling hdr->release() directly.

This can be reproduced (sometimes) by performing "storage failover takeover" commands on NetApp filer while doing direct I/O from a client.

This can also be reproduced using SystemTap to simulate a failure while doing direct I/O from a client (from Dave Wysochanski <[email protected]>):

stap -v -g -e 'probe module("nfs_layout_nfsv41_files").function("nfs4_fl_prepare_ds").return { $return=NULL; exit(); }'

---
 fs/nfs/pnfs.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -2145,7 +2145,7 @@ pnfs_write_through_mds(struct nfs_pageio
 		nfs_pageio_reset_write_mds(desc);
 		mirror->pg_recoalesce = 1;
 	}
-	hdr->release(hdr);
+	hdr->completion_ops->completion(hdr);
 }
 
 static enum pnfs_try_status

@@ -2256,7 +2256,7 @@ pnfs_read_through_mds(struct nfs_pageio_
 		nfs_pageio_reset_read_mds(desc);
 		mirror->pg_recoalesce = 1;
 	}
-	hdr->release(hdr);
+	hdr->completion_ops->completion(hdr);
 }
 
 /*

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/nfs-pnfs-fix-nfs_direct_req-ref-leak-when-i-o-falls-back-to-the-mds.patch