storage/posix: Do not fail entry creation fops if gfid handle already exists

PROBLEM:
tests/bugs/shard/bug-1251824.t fails occasionally with EIO due to gfid
mismatch across replicas on the same shard when dd is executed.

CAUSE:
Turns out this is due to a race between posix_mknod() and posix_lookup().

posix mknod does 3 operations, among other things:
1. creation of the entry itself under its parent directory
2. setting the gfid xattr on the file, and
3. creating the gfid link under .glusterfs.

Consider a case where the thread doing posix_mknod() (initiated by shard)
has executed steps 1 and 2 and is on its way to executing 3. And a
parallel LOOKUP from another thread on noting that loc->inode->gfid is NULL,
tries to perform gfid_heal where it attempts to create the gfid link
under .glusterfs and succeeds.  As a result, posix_gfid_set() through
MKNOD (step 3) fails with EEXIST.

In the older code, MKNOD under such conditions was NOT being treated
as a failure. But commit e37ee6d changes this behavior by failing MKNOD,
causing the entry creation to be undone in posix_mknod() (it's another
matter that the stale gfid handle gets left behind if lookup has gone
ahead and gfid-healed it).
All of this happens on only one replica while on the other MKNOD succeeds.

Now if a parallel write causes shard translator to send another MKNOD
of the same shard (shortly after AFR releases entrylk from the first
MKNOD), the file is created on the other replica too, although with a
new gfid (since "gfid-req" that is passed now is a new UUID. This leads
to a gfid-mismatch across the replicas.

FIX:
The solution is to not fail MKNOD (or any other entry fop for that matter
that does posix_gfid_set()) if the .glusterfs link creation fails with EEXIST.

Change-Id: I84a5e54d214b6c47ed85671a880bb1c767a29f4d
fixes: bz#1638453
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>

2 files changed, 16 insertions, 6 deletions

diff --git a/xlators/storage/posix/src/posix-handle.c b/xlators/storage/posix/src/posix-handle.c
index bc34e3e5dba..5c50d413640 100644
--- a/xlators/storage/posix/src/posix-handle.c
+++ b/xlators/storage/posix/src/posix-handle.c
@@ -741,6 +741,7 @@ posix_handle_hard(xlator_t *this, const char *oldpath, uuid_t gfid,
     char *newpath = NULL;
     struct stat newbuf;
     int ret = -1;
+    gf_boolean_t link_exists = _gf_false;
 
     MAKE_HANDLE_ABSPATH(newpath, this, gfid);
 
@@ -762,11 +763,15 @@ posix_handle_hard(xlator_t *this, const char *oldpath, uuid_t gfid,
         ret = sys_link(oldpath, newpath);
 
         if (ret) {
-            gf_msg(this->name, GF_LOG_WARNING, errno, P_MSG_HANDLE_CREATE,
-                   "link %s -> %s"
-                   "failed ",
-                   oldpath, newpath);
-            return -1;
+            if (errno != EEXIST) {
+                gf_msg(this->name, GF_LOG_WARNING, errno, P_MSG_HANDLE_CREATE,
+                       "link %s -> %s"
+                       "failed ",
+                       oldpath, newpath);
+                return -1;
+            } else {
+                link_exists = _gf_true;
+            }
         }
 
         ret = sys_lstat(newpath, &newbuf);
@@ -775,6 +780,11 @@ posix_handle_hard(xlator_t *this, const char *oldpath, uuid_t gfid,
                    "lstat on %s failed", newpath);
             return -1;
         }
+        if ((link_exists) && (!S_ISREG(newbuf.st_mode))) {
+            gf_msg(this->name, GF_LOG_ERROR, EINVAL, P_MSG_HANDLE_CREATE,
+                   "%s - Expected regular file", newpath);
+            return -1;
+        }
     }
 
     if (newbuf.st_ino != oldbuf->st_ino || newbuf.st_dev != oldbuf->st_dev) {
diff --git a/xlators/storage/posix/src/posix-helpers.c b/xlators/storage/posix/src/posix-helpers.c
index 4c3f064f564..9bb3b994aa0 100644
--- a/xlators/storage/posix/src/posix-helpers.c
+++ b/xlators/storage/posix/src/posix-helpers.c
@@ -962,7 +962,7 @@ posix_gfid_set(xlator_t *this, const char *path, loc_t *loc, dict_t *xattr_req,
     if (sys_lstat(path, &stat) != 0) {
         ret = -1;
         gf_msg(this->name, GF_LOG_ERROR, errno, P_MSG_LSTAT_FAILED,
-               "lsatat on %s failed", path);
+               "lstat on %s failed", path);
         goto out;
     }