syncop: Change return value of syncop

Problem:
We found a day-1 bug when syncop_xxx() infra is used inside a synctask with
compilation optimization (CFLAGS -O2).

Detailed explanation of the Root cause:
We found the bug in 'gf_defrag_migrate_data' in rebalance operation:

Lets look at interesting parts of the function:

int
gf_defrag_migrate_data (xlator_t *this, gf_defrag_info_t *defrag, loc_t *loc,
                        dict_t *migrate_data)
{
.....
code section - [ Loop ]
        while ((ret = syncop_readdirp (this, fd, 131072, offset, NULL,
                                       &entries)) != 0) {
.....
code section - [ ERRNO-1 ] (errno of readdirp is stored in readdir_operrno by a
thread)
                /* Need to keep track of ENOENT errno, that means, there is no
                   need to send more readdirp() */
                readdir_operrno = errno;
.....
code section - [ SYNCOP-1 ] (syncop_getxattr is called by a thread)
                        ret = syncop_getxattr (this, &entry_loc, &dict,
                                               GF_XATTR_LINKINFO_KEY);
code section - [ ERRNO-2]   (checking for failures of syncop_getxattr(). This
may not always be executed in same thread which executed [SYNCOP-1])
                        if (ret < 0) {
                                if (errno != ENODATA) {
                                        loglevel = GF_LOG_ERROR;
                                        defrag->total_failures += 1;
.....
}

the function above could be executed by thread(t1) till [SYNCOP-1] and code
from [ERRNO-2] can be executed by a different thread(t2) because of the way
syncop-infra schedules the tasks.

when the code is compiled with -O2 optimization this is the assembly code that
is generated:
 [ERRNO-1]
1165                        readdir_operrno = errno; <<---- errno gets expanded
as *(__errno_location())
   0x00007fd149d48b60 <+496>:        callq  0x7fd149d410c0 <address@hidden>
   0x00007fd149d48b72 <+514>:        mov    %rax,0x50(%rsp) <<------ Address
returned by __errno_location() is stored in a special location in stack for
later use.
   0x00007fd149d48b77 <+519>:        mov    (%rax),%eax
   0x00007fd149d48b79 <+521>:        mov    %eax,0x78(%rsp)
....
 [ERRNO-2]
1281                                        if (errno != ENODATA) {
   0x00007fd149d492ae <+2366>:        mov    0x50(%rsp),%rax <<-----  Because
it already stored the address returned by __errno_location(), it just
dereferences the address to get the errno value. BUT THIS CODE NEED NOT BE
EXECUTED BY SAME THREAD!!!
   0x00007fd149d492b3 <+2371>:        mov    $0x9,%ebp
   0x00007fd149d492b8 <+2376>:        mov    (%rax),%edi
   0x00007fd149d492ba <+2378>:        cmp    $0x3d,%edi

The problem is that __errno_location() value of t1 and t2 are different. So
[ERRNO-2] ends up reading errno of t1 instead of errno of t2 even though t2 is
executing [ERRNO-2] code section.

When code is compiled without any optimization for [ERRNO-2]:
1281                                        if (errno != ENODATA) {
   0x00007fd58e7a326f <+2237>:        callq  0x7fd58e797300
<address@hidden><<--- As it is calling __errno_location() again it gets the
location from t2 so it works as intended.
   0x00007fd58e7a3274 <+2242>:        mov    (%rax),%eax
   0x00007fd58e7a3276 <+2244>:        cmp    $0x3d,%eax
   0x00007fd58e7a3279 <+2247>:        je     0x7fd58e7a32a1
<gf_defrag_migrate_data+2287>

Fix:
Make syncop_xxx() return (-errno) value as the return value in
case of errors and all the functions which make syncop_xxx() will need to use
(-ret) to figure out the reason for failure in case of syncop_xxx() failures.

Change-Id: I314d20dabe55d3e62ff66f3b4adb1cac2eaebb57
BUG: 1040356
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/6475
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/api/src/glfs-handleops.c b/api/src/glfs-handleops.c
index 0f996d3a2..5bba38b5f 100644
--- a/api/src/glfs-handleops.c
+++ b/api/src/glfs-handleops.c
@@ -152,6 +152,7 @@ glfs_h_stat (struct glfs *fs, struct glfs_object *object, struct stat *stat)
 
 	/* fop/op */
 	ret = syncop_stat (subvol, &loc, &iatt);
+        DECODE_SYNCOP_ERR (ret);
 
 	/* populate out args */
 	if (!ret && stat) {
@@ -258,6 +259,7 @@ glfs_h_setattrs (struct glfs *fs, struct glfs_object *object, struct stat *stat,
 
 	/* fop/op */
 	ret = syncop_setattr (subvol, &loc, &iatt, glvalid, 0, 0);
+        DECODE_SYNCOP_ERR (ret);
 out:
 	loc_wipe (&loc);
 
@@ -331,6 +333,7 @@ glfs_h_open (struct glfs *fs, struct glfs_object *object, int flags)
 
 	/* fop/op */
 	ret = syncop_open (subvol, &loc, flags, glfd->fd);
+        DECODE_SYNCOP_ERR (ret);
 
 out:
 	loc_wipe (&loc);
@@ -420,6 +423,7 @@ glfs_h_creat (struct glfs *fs, struct glfs_object *parent, const char *path,
 	/* fop/op */
 	ret = syncop_create (subvol, &loc, flags, mode, glfd->fd,
 			     xattr_req, &iatt);
+        DECODE_SYNCOP_ERR (ret);
 
 	/* populate out args */
 	if (ret == 0) {
@@ -518,6 +522,7 @@ glfs_h_mkdir (struct glfs *fs, struct glfs_object *parent, const char *path,
 
 	/* fop/op */
 	ret = syncop_mkdir (subvol, &loc, mode, xattr_req, &iatt);
+        DECODE_SYNCOP_ERR (ret);
 
 	/* populate out args */
 	if ( ret == 0 )  {
@@ -606,6 +611,7 @@ glfs_h_mknod (struct glfs *fs, struct glfs_object *parent, const char *path,
 
 	/* fop/op */
 	ret = syncop_mknod (subvol, &loc, mode, dev, xattr_req, &iatt);
+        DECODE_SYNCOP_ERR (ret);
 
 	/* populate out args */
 	if (ret == 0) {
@@ -676,11 +682,13 @@ glfs_h_unlink (struct glfs *fs, struct glfs_object *parent, const char *path)
 
 	if (!IA_ISDIR(loc.inode->ia_type)) {
 		ret = syncop_unlink (subvol, &loc);
+                DECODE_SYNCOP_ERR (ret);
 		if (ret != 0) {
 			goto out;
 		}
 	} else {
 		ret = syncop_rmdir (subvol, &loc, 0);
+                DECODE_SYNCOP_ERR (ret);
 		if (ret != 0) {
 			goto out;
 		}
@@ -755,6 +763,7 @@ glfs_h_opendir (struct glfs *fs, struct glfs_object *object)
 
 	/* fop/op */
 	ret = syncop_opendir (subvol, &loc, glfd->fd);
+        DECODE_SYNCOP_ERR (ret);
 
 out:
 	loc_wipe (&loc);
@@ -846,6 +855,7 @@ glfs_h_create_from_handle (struct glfs *fs, unsigned char *handle, int len,
 	}
 
 	ret = syncop_lookup (subvol, &loc, 0, &iatt, 0, 0);
+        DECODE_SYNCOP_ERR (ret);
 	if (ret) {
 		gf_log (subvol->name, GF_LOG_WARNING,
 			"inode refresh of %s failed: %s",
@@ -934,6 +944,7 @@ glfs_h_truncate (struct glfs *fs, struct glfs_object *object, off_t offset)
 
 	/* fop/op */
 	ret = syncop_truncate (subvol, &loc, (off_t)offset);
+        DECODE_SYNCOP_ERR (ret);
 
 	/* populate out args */
 	if (ret == 0)
@@ -1006,6 +1017,7 @@ glfs_h_symlink (struct glfs *fs, struct glfs_object *parent, const char *name,
 
 	/* fop/op */
 	ret = syncop_symlink (subvol, &loc, data, xattr_req, &iatt);
+        DECODE_SYNCOP_ERR (ret);
 
 	/* populate out args */
 	if (ret == 0) {
@@ -1081,6 +1093,7 @@ glfs_h_readlink (struct glfs *fs, struct glfs_object *object, char *buf,
 
 	/* fop/op */
 	ret = syncop_readlink (subvol, &loc, &linkval, bufsiz);
+        DECODE_SYNCOP_ERR (ret);
 
 	/* populate out args */
 	if (ret > 0)
@@ -1166,6 +1179,7 @@ glfs_h_link (struct glfs *fs, struct glfs_object *linksrc,
 
 	/* fop/op */
 	ret = syncop_link (subvol, &oldloc, &newloc);
+        DECODE_SYNCOP_ERR (ret);
 
 	if (ret == 0)
 		/* TODO: No iatt to pass as there has been no lookup */
@@ -1256,6 +1270,7 @@ glfs_h_rename (struct glfs *fs, struct glfs_object *olddir, const char *oldname,
 	/* TODO: check if new or old is a prefix of the other, and fail EINVAL */
 
 	ret = syncop_rename (subvol, &oldloc, &newloc);
+        DECODE_SYNCOP_ERR (ret);
 
 	if (ret == 0)
 		inode_rename (oldloc.parent->table, oldloc.parent, oldloc.name,