linux-kernel - [PATCH 3.16 129/410] nfs/pnfs: fix nfs_direct_req ref leak when i/o falls back to the mds

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Message-ID: <lsq.1528380321.59515711@decadent.org.uk>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Scott Mayhew" <smayhew@...hat.com>,
        "Trond Myklebust" <trond.myklebust@...marydata.com>
Subject: [PATCH 3.16 129/410] nfs/pnfs: fix nfs_direct_req ref leak when
 i/o falls back to the mds

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Scott Mayhew <smayhew@...hat.com>

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
<dwysocha@...hat.com>):

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

Suggested-by: Trond Myklebust <trond.myklebust@...marydata.com>
Signed-off-by: Scott Mayhew <smayhew@...hat.com>
Fixes: 1ca018d28d ("pNFS: Fix a memory leak when attempted pnfs fails")
Signed-off-by: Trond Myklebust <trond.myklebust@...marydata.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/nfs/pnfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -1557,7 +1557,7 @@ pnfs_write_through_mds(struct nfs_pageio
 		nfs_pageio_reset_write_mds(desc);
 		desc->pg_recoalesce = 1;
 	}
-	hdr->release(hdr);
+	hdr->completion_ops->completion(hdr);
 }

 static enum pnfs_try_status
@@ -1694,7 +1694,7 @@ pnfs_read_through_mds(struct nfs_pageio_
 		nfs_pageio_reset_read_mds(desc);
 		desc->pg_recoalesce = 1;
 	}
-	hdr->release(hdr);
+	hdr->completion_ops->completion(hdr);
 }

 /*