[PATCH] pnfs: fix race in filelayout commit path

[Weston Andros Adamson <dros@primarydata.com>]

Hold the lock while changing wlseg in filelayout_recover_commit_reqs.

The following oops can be reproduced by running iozone for a while against
a 2 DS pynfs filelayout server.

general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC
Modules linked in: nfs_layout_nfsv41_files rpcsec_gss_krb5 nfsv4 nfs fscache
CPU: 0 PID: 903 Comm: iozone Not tainted 3.15.0-rc1-branch-dros_testing+ #44
Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference
task: ffff880078164480 ti: ffff88006e972000 task.ti: ffff88006e972000
RIP: 0010:[<ffffffffa01936e1>]  [<ffffffffa01936e1>] nfs_init_commit+0x22/0x
RSP: 0018:ffff88006e973d30  EFLAGS: 00010246
RAX: ffff88006e973e00 RBX: ffff88006e828800 RCX: ffff88006e973e10
RDX: 0000000000000000 RSI: ffff88006e973e00 RDI: dead4ead00000000
RBP: ffff88006e973d38 R08: ffff88006e8289d8 R09: 0000000000000000
R10: ffff88006e8289d8 R11: 0000000000016988 R12: ffff88006e973b98
R13: ffff88007a0a6648 R14: ffff88006e973e10 R15: ffff88006e828800
FS:  00007f2ce396b740(0000) GS:ffff88007f200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f03278a1000 CR3: 0000000079043000 CR4: 00000000001407f0
Stack:
ffff88006e8289d8 ffff88006e973da8 ffffffffa00f144f ffff88006e9478c0
ffff88006e973e00 ffff88006de21080 0000000100000002 ffff880079be6c48
ffff88006e973d70 ffff88006e973d70 ffff88006e973e10 ffff88006de21080
Call Trace:
[<ffffffffa00f144f>] filelayout_commit_pagelist+0x1ae/0x34a [nfs_layout_nfsv
[<ffffffffa0194f72>] nfs_generic_commit_list+0x92/0xc4 [nfs]
[<ffffffffa0195053>] nfs_commit_inode+0xaf/0x114 [nfs]
[<ffffffffa01892bd>] nfs_file_fsync_commit+0x82/0xbe [nfs]
[<ffffffffa01ceb0d>] nfs4_file_fsync+0x59/0x9b [nfsv4]
[<ffffffff8114ee3c>] vfs_fsync_range+0x18/0x20
[<ffffffff8114ee60>] vfs_fsync+0x1c/0x1e
[<ffffffffa01891c2>] nfs_file_flush+0x7f/0x84 [nfs]
[<ffffffff81127a43>] filp_close+0x3c/0x72
[<ffffffff81140e12>] __close_fd+0x82/0x9a
[<ffffffff81127a9c>] SyS_close+0x23/0x4c
[<ffffffff814acd12>] system_call_fastpath+0x16/0x1b
Code: 5b 41 5c 41 5d 41 5e 5d c3 0f 1f 44 00 00 55 48 89 e5 53 48 89 fb 48 8
RIP  [<ffffffffa01936e1>] nfs_init_commit+0x22/0xe1 [nfs]
RSP <ffff88006e973d30>
---[ end trace 732fe6419b235e2f ]---

Suggested-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
---

Minor change applied to Trond's suggested fix. Should we add a signed-off-by
line for Trond too?

 fs/nfs/nfs4filelayout.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/nfs4filelayout.c b/fs/nfs/nfs4filelayout.c
index b9a35c0..aa9172d 100644
--- a/fs/nfs/nfs4filelayout.c
+++ b/fs/nfs/nfs4filelayout.c
@@ -1220,15 +1220,18 @@ static void filelayout_recover_commit_reqs(struct list_head *dst,
 					   struct nfs_commit_info *cinfo)
 {
 	struct pnfs_commit_bucket *b;
+	struct pnfs_layout_segment *lseg;
 	int i;
 
+restart:
 	spin_lock(cinfo->lock);
 	for (i = 0, b = cinfo->ds->buckets; i < cinfo->ds->nbuckets; i++, b++) {
 		if (transfer_commit_list(&b->written, dst, cinfo, 0)) {
-			spin_unlock(cinfo->lock);
-			pnfs_put_lseg(b->wlseg);
+			lseg = b->wlseg;
 			b->wlseg = NULL;
-			spin_lock(cinfo->lock);
+			spin_unlock(cinfo->lock);
+			pnfs_put_lseg(lseg);
+			goto restart;
 		}
 	}
 	cinfo->ds->nwritten = 0;
-- 
1.8.5.2 (Apple Git-48)