Fix race between read-ahead and write.

Change-Id: I0ed1aca585733302b5e3840f392849e12f0b0f0d
BUG: 783313
Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-on: http://review.gluster.com/2666
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@gluster.com>

3 files changed, 68 insertions, 26 deletions

diff --git a/xlators/performance/read-ahead/src/page.c b/xlators/performance/read-ahead/src/page.c
index 9778ef542..0c9a61853 100644
--- a/xlators/performance/read-ahead/src/page.c
+++ b/xlators/performance/read-ahead/src/page.c
@@ -175,14 +175,8 @@ ra_fault_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 if (op_ret >= 0)
                         file->stbuf = *stbuf;
 
-                if (op_ret < 0) {
-                        page = ra_page_get (file, pending_offset);
-                        if (page)
-                                waitq = ra_page_error (page, op_ret, op_errno);
-                        goto unlock;
-                }
-
                 page = ra_page_get (file, pending_offset);
+
                 if (!page) {
                         gf_log (this->name, GF_LOG_TRACE,
                                 "wasted copy: %"PRId64"[+%"PRId64"] file=%p",
@@ -190,6 +184,29 @@ ra_fault_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                         goto unlock;
                 }
 
+                /*
+                 * "Dirty" means that the request was a pure read-ahead; it's
+                 * set for requests we issue ourselves, and cleared when user
+                 * requests are issued or put on the waitq.  "Poisoned" means
+                 * that we got a write while a read was still in flight, and we
+                 * couldn't stop it so we marked it instead.  If it's both
+                 * dirty and poisoned by the time we get here, we cancel its
+                 * effect so that a subsequent user read doesn't get data that
+                 * we know is stale (because we made it stale ourselves).  We
+                 * can't use ESTALE because that has special significance.
+                 * ECANCELED has no such special meaning, and is close to what
+                 * we're trying to indicate.
+                 */
+                if (page->dirty && page->poisoned) {
+                        op_ret = -1;
+                        op_errno = ECANCELED;
+                }
+
+                if (op_ret < 0) {
+                        waitq = ra_page_error (page, op_ret, op_errno);
+                        goto unlock;
+                }
+
                 if (page->vector) {
                         iobref_unref (page->iobref);
                         GF_FREE (page->vector);
diff --git a/xlators/performance/read-ahead/src/read-ahead.c b/xlators/performance/read-ahead/src/read-ahead.c
index 37f34f2eb..928d8b7bd 100644
--- a/xlators/performance/read-ahead/src/read-ahead.c
+++ b/xlators/performance/read-ahead/src/read-ahead.c
@@ -231,7 +231,8 @@ ra_create (call_frame_t *frame, xlator_t *this, loc_t *loc, int32_t flags,
 */
 
 static void
-flush_region (call_frame_t *frame, ra_file_t *file, off_t offset, off_t size)
+flush_region (call_frame_t *frame, ra_file_t *file, off_t offset, off_t size,
+              int for_write)
 {
         ra_page_t *trav = NULL;
         ra_page_t *next = NULL;
@@ -243,8 +244,13 @@ flush_region (call_frame_t *frame, ra_file_t *file, off_t offset, off_t size)
                        && trav->offset < (offset + size)) {
 
                         next = trav->next;
-                        if (trav->offset >= offset && !trav->waitq) {
-                                ra_page_purge (trav);
+                        if (trav->offset >= offset) {
+                                if (!trav->waitq) {
+                                        ra_page_purge (trav);
+                                }
+                                else if (for_write) {
+                                        trav->poisoned = 1;
+                                }
                         }
                         trav = next;
                 }
@@ -392,15 +398,15 @@ dispatch_requests (call_frame_t *frame, ra_file_t *file)
                         trav = ra_page_get (file, trav_offset);
                         if (!trav) {
                                 trav = ra_page_create (file, trav_offset);
+                                if (!trav) {
+                                        local->op_ret = -1;
+                                        local->op_errno = ENOMEM;
+                                        goto unlock;
+                                }
                                 fault = 1;
                                 need_atime_update = 0;
                         }
-
-                        if (!trav) {
-                                local->op_ret = -1;
-                                local->op_errno = ENOMEM;
-                                goto unlock;
-                        }
+                        trav->dirty = 0;
 
                         if (trav->ready) {
                                 gf_log (frame->this->name, GF_LOG_TRACE,
@@ -513,7 +519,7 @@ ra_readv (call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
         }
 
         if (!expected_offset) {
-                flush_region (frame, file, 0, file->pages.prev->offset + 1);
+                flush_region (frame, file, 0, file->pages.prev->offset + 1, 0);
         }
 
         local = (void *) GF_CALLOC (1, sizeof (*local), gf_ra_mt_ra_local_t);
@@ -536,7 +542,7 @@ ra_readv (call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
 
         dispatch_requests (frame, file);
 
-        flush_region (frame, file, 0, floor (offset, file->page_size));
+        flush_region (frame, file, 0, floor (offset, file->page_size), 0);
 
         read_ahead (frame, file);
 
@@ -596,7 +602,7 @@ ra_flush (call_frame_t *frame, xlator_t *this, fd_t *fd)
 
         file = (ra_file_t *)(long)tmp_file;
         if (file) {
-                flush_region (frame, file, 0, file->pages.prev->offset+1);
+                flush_region (frame, file, 0, file->pages.prev->offset+1, 0);
         }
 
         STACK_WIND (frame, ra_flush_cbk, FIRST_CHILD (this),
@@ -624,7 +630,7 @@ ra_fsync (call_frame_t *frame, xlator_t *this, fd_t *fd, int32_t datasync)
 
         file = (ra_file_t *)(long)tmp_file;
         if (file) {
-                flush_region (frame, file, 0, file->pages.prev->offset+1);
+                flush_region (frame, file, 0, file->pages.prev->offset+1, 0);
         }
 
         STACK_WIND (frame, ra_fsync_cbk, FIRST_CHILD (this),
@@ -649,7 +655,7 @@ ra_writev_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         file = frame->local;
 
         if (file) {
-                flush_region (frame, file, 0, file->pages.prev->offset+1);
+                flush_region (frame, file, 0, file->pages.prev->offset+1, 1);
         }
 
         frame->local = NULL;
@@ -673,7 +679,7 @@ ra_writev (call_frame_t *frame, xlator_t *this, fd_t *fd, struct iovec *vector,
         fd_ctx_get (fd, this, &tmp_file);
         file = (ra_file_t *)(long)tmp_file;
         if (file) {
-                flush_region (frame, file, 0, file->pages.prev->offset+1);
+                flush_region (frame, file, 0, file->pages.prev->offset+1, 1);
                 frame->local = file;
                 /* reset the read-ahead counters too */
                 file->expected = file->page_count = 0;
@@ -739,8 +745,16 @@ ra_truncate (call_frame_t *frame, xlator_t *this, loc_t *loc, off_t offset)
 
                         if (!file)
                                 continue;
+                        /*
+                         * Truncation invalidates reads just like writing does.
+                         * TBD: this seems to flush more than it should.  The
+                         * only time we should flush at all is when we're
+                         * shortening (not lengthening) the file, and then only
+                         * from new EOF to old EOF.  The same problem exists in
+                         * ra_ftruncate.
+                         */
                         flush_region (frame, file, 0,
-                                      file->pages.prev->offset + 1);
+                                      file->pages.prev->offset + 1, 1);
                 }
         }
         UNLOCK (&inode->lock);
@@ -775,6 +789,8 @@ ra_page_dump (struct ra_page *page)
 
         gf_proc_dump_write ("dirty", "%s", page->dirty ? "yes" : "no");
 
+        gf_proc_dump_write ("poisoned", "%s", page->poisoned ? "yes" : "no");
+
         gf_proc_dump_write ("ready", "%s", page->ready ? "yes" : "no");
 
         for (trav = page->waitq; trav; trav = trav->next) {
@@ -870,7 +886,7 @@ ra_fstat (call_frame_t *frame, xlator_t *this, fd_t *fd)
                         if (!file)
                                 continue;
                         flush_region (frame, file, 0,
-                                      file->pages.prev->offset + 1);
+                                      file->pages.prev->offset + 1, 0);
                 }
         }
         UNLOCK (&inode->lock);
@@ -907,8 +923,16 @@ ra_ftruncate (call_frame_t *frame, xlator_t *this, fd_t *fd, off_t offset)
                         file = (ra_file_t *)(long)tmp_file;
                         if (!file)
                                 continue;
+                        /*
+                         * Truncation invalidates reads just like writing does.
+                         * TBD: this seems to flush more than it should.  The
+                         * only time we should flush at all is when we're
+                         * shortening (not lengthening) the file, and then only
+                         * from new EOF to old EOF.  The same problem exists in
+                         * ra_truncate.
+                         */
                         flush_region (frame, file, 0,
-                                      file->pages.prev->offset + 1);
+                                      file->pages.prev->offset + 1, 1);
                 }
         }
         UNLOCK (&inode->lock);
diff --git a/xlators/performance/read-ahead/src/read-ahead.h b/xlators/performance/read-ahead/src/read-ahead.h
index d0bbcde81..f5e73cb66 100644
--- a/xlators/performance/read-ahead/src/read-ahead.h
+++ b/xlators/performance/read-ahead/src/read-ahead.h
@@ -76,7 +76,8 @@ struct ra_page {
         struct ra_page   *next;
         struct ra_page   *prev;
         struct ra_file   *file;
-        char              dirty;
+        char              dirty;    /* Internal request, not from user. */
+        char              poisoned; /* Pending read invalidated by write. */
         char              ready;
         struct iovec     *vector;
         int32_t           count;