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, 31 insertions, 13 deletions

diff --git a/xlators/cluster/afr/src/afr-self-heald.c b/xlators/cluster/afr/src/afr-self-heald.c
index 5f85c3047d4..9e5c1b3e79f 100644
--- a/xlators/cluster/afr/src/afr-self-heald.c
+++ b/xlators/cluster/afr/src/afr-self-heald.c
@@ -336,8 +336,9 @@ _get_path_from_gfid_loc (xlator_t *this, xlator_t *readdir_xl, loc_t *child,
 
         ret = syncop_getxattr (readdir_xl, child, &xattr, GFID_TO_PATH_KEY);
         if (ret < 0) {
-                if ((errno == ENOENT || errno == ESTALE) && missing)
+                if ((-ret == ENOENT || -ret == ESTALE) && missing)
                         *missing = _gf_true;
+                ret = -1;
                 goto out;
         }
         ret = dict_get_str (xattr, GFID_TO_PATH_KEY, &path);
@@ -437,10 +438,10 @@ _remove_stale_index (xlator_t *this, xlator_t *readdir_xl,
         gf_log (this->name, GF_LOG_DEBUG, "Removing stale index "
                 "for %s on %s", index_loc.name, readdir_xl->name);
         ret = syncop_unlink (readdir_xl, &index_loc);
-        if(ret && (errno != ENOENT)) {
+        if((ret < 0) && (-ret != ENOENT)) {
                 gf_log(this->name, GF_LOG_ERROR, "%s: Failed to remove index "
                        "on %s - %s",index_loc.name, readdir_xl->name,
-                       strerror (errno));
+                       strerror (-ret));
         }
         index_loc.path = NULL;
         loc_wipe (&index_loc);
@@ -467,8 +468,10 @@ _count_hard_links_under_base_indices_dir (xlator_t *this,
         child = crawl_data->child;
 
         ret = syncop_lookup (readdir_xl, childloc, NULL, iattr, NULL, &parent);
-        if (ret)
+        if (ret) {
+                ret = -1;
                 goto out;
+        }
 
         ret = dict_get_int32 (output, this->name, &xl_id);
         if (ret)
@@ -648,8 +651,10 @@ _self_heal_entry (xlator_t *this, afr_crawl_data_t *crawl_data, gf_dirent_t *ent
 
         ret = syncop_lookup (this, child, xattr_req,
                              iattr, &xattr_rsp, &parentbuf);
-        _crawl_post_sh_action (this, parent, child, ret, errno, xattr_rsp,
+        _crawl_post_sh_action (this, parent, child, ret, -ret, xattr_rsp,
                                crawl_data);
+        if (ret < 0)
+                ret = -1;
         if (xattr_rsp)
                 dict_unref (xattr_rsp);
         if (ret == 0)
@@ -1190,8 +1195,10 @@ afr_crawl_build_start_loc (xlator_t *this, afr_crawl_data_t *crawl_data,
                 afr_build_root_loc (this, &rootloc);
                 ret = syncop_getxattr (readdir_xl, &rootloc, &xattr,
                                        GF_XATTROP_INDEX_GFID);
-                if (ret < 0)
+                if (ret < 0) {
+                        ret = -1;
                         goto out;
+                }
                 ret = dict_get_ptr (xattr, GF_XATTROP_INDEX_GFID, &index_gfid);
                 if (ret < 0) {
                         gf_log (this->name, GF_LOG_ERROR, "failed to get index "
@@ -1210,11 +1217,12 @@ afr_crawl_build_start_loc (xlator_t *this, afr_crawl_data_t *crawl_data,
                 ret = syncop_lookup (readdir_xl, dirloc, NULL,
                                      &iattr, NULL, &parent);
                 if (ret < 0) {
-                        if (errno != ENOENT) {
+                        if (-ret != ENOENT) {
                                 gf_log (this->name, GF_LOG_ERROR, "lookup "
                                         "failed on index dir on %s - (%s)",
-                                        readdir_xl->name, strerror (errno));
+                                        readdir_xl->name, strerror (-ret));
                         }
+                        ret = -1;
                         goto out;
                 }
                 ret = _link_inode_update_loc (this, dirloc, &iattr);
@@ -1224,8 +1232,10 @@ afr_crawl_build_start_loc (xlator_t *this, afr_crawl_data_t *crawl_data,
                 afr_build_root_loc (this, &rootloc);
                 ret = syncop_getxattr (readdir_xl, &rootloc, &xattr,
                                        GF_BASE_INDICES_HOLDER_GFID);
-                if (ret < 0)
+                if (ret < 0) {
+                        ret = -1;
                         goto out;
+                }
                 ret = dict_get_ptr (xattr, GF_BASE_INDICES_HOLDER_GFID,
                                     &base_indices_holder_vgfid);
                 if (ret < 0) {
@@ -1246,16 +1256,17 @@ afr_crawl_build_start_loc (xlator_t *this, afr_crawl_data_t *crawl_data,
                 ret = syncop_lookup (readdir_xl, dirloc, NULL, &iattr, NULL,
                                      &parent);
                 if (ret < 0) {
-                        if (errno != ENOENT) {
+                        if (-ret != ENOENT) {
                                 gf_log (this->name, GF_LOG_ERROR, "lookup "
                                         "failed for base_indices_holder dir"
                                         " on %s - (%s)", readdir_xl->name,
-                                        strerror (errno));
+                                        strerror (-ret));
 
                         } else {
                                 gf_log (this->name, GF_LOG_ERROR, "base_indices"
                                         "_holder is not yet created.");
                         }
+                        ret = -1;
                         goto out;
                 }
                 ret = _link_inode_update_loc (this, dirloc, &iattr);
@@ -1290,6 +1301,7 @@ afr_crawl_opendir (xlator_t *this, afr_crawl_data_t *crawl_data, fd_t **dirfd,
                 if (ret < 0) {
                         gf_log (this->name, GF_LOG_ERROR,
                                 "opendir failed on %s", dirloc->path);
+                        ret = -1;
                         goto out;
                 }
         } else {
@@ -1442,8 +1454,13 @@ _crawl_directory (fd_t *fd, loc_t *loc, afr_crawl_data_t *crawl_data)
                 else
                         ret = syncop_readdir (readdir_xl, fd, 131072, offset,
                                               &entries);
-                if (ret <= 0)
+                if (ret < 0) {
+                        ret = -1;
+                        break;
+                } else if (ret == 0) {
                         break;
+                }
+
                 ret = 0;
                 free_entries = _gf_true;
 
@@ -1503,7 +1520,8 @@ afr_find_child_position (xlator_t *this, int child, afr_child_pos_t *pos)
                                GF_XATTR_NODE_UUID_KEY);
         if (ret < 0) {
                 gf_log (this->name, GF_LOG_ERROR, "getxattr failed on %s - "
-                        "(%s)", priv->children[child]->name, strerror (errno));
+                        "(%s)", priv->children[child]->name, strerror (-ret));
+                ret = -1;
                 goto out;
         }