From 1ebf980127924c639e2b85c08468311ba1c95b70 Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Thu, 20 Jul 2017 17:00:02 -0400 Subject: [PATCH] NFS/filelayout: Fix racy setting of fl->dsaddr in filelayout_check_deviceid() We must set fl->dsaddr once, and once only, even if there are multiple processes calling filelayout_check_deviceid() for the same layout segment. Reported-by: Olga Kornievskaia Signed-off-by: Trond Myklebust Signed-off-by: Anna Schumaker --- fs/nfs/filelayout/filelayout.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/fs/nfs/filelayout/filelayout.c b/fs/nfs/filelayout/filelayout.c index 080fc6b278bd..44c638b7876c 100644 --- a/fs/nfs/filelayout/filelayout.c +++ b/fs/nfs/filelayout/filelayout.c @@ -542,6 +542,10 @@ filelayout_check_deviceid(struct pnfs_layout_hdr *lo, struct nfs4_file_layout_dsaddr *dsaddr; int status = -EINVAL; + /* Is the deviceid already set? If so, we're good. */ + if (fl->dsaddr != NULL) + return 0; + /* find and reference the deviceid */ d = nfs4_find_get_deviceid(NFS_SERVER(lo->plh_inode), &fl->deviceid, lo->plh_lc_cred, gfp_flags); @@ -553,8 +557,6 @@ filelayout_check_deviceid(struct pnfs_layout_hdr *lo, if (filelayout_test_devid_unavailable(&dsaddr->id_node)) goto out_put; - fl->dsaddr = dsaddr; - if (fl->first_stripe_index >= dsaddr->stripe_count) { dprintk("%s Bad first_stripe_index %u\n", __func__, fl->first_stripe_index); @@ -570,6 +572,13 @@ filelayout_check_deviceid(struct pnfs_layout_hdr *lo, goto out_put; } status = 0; + + /* + * Atomic compare and xchange to ensure we don't scribble + * over a non-NULL pointer. + */ + if (cmpxchg(&fl->dsaddr, NULL, dsaddr) != NULL) + goto out_put; out: return status; out_put: