gfs2: add some missing log locking

Function gfs2_logd() calls the log flushing functions gfs2_ail1_start(),
gfs2_ail1_wait(), and gfs2_ail1_empty() without holding sdp->sd_log_flush_lock,
but these functions require exclusion against concurrent transactions.

To fix that, add a non-locking __gfs2_log_flush() function.  Then, in
gfs2_logd(), take sdp->sd_log_flush_lock before calling the above mentioned log
flushing functions and __gfs2_log_flush().

Fixes: 5e4c763 ("gfs2: Issue revokes more intelligently")
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

Author: Andreas Gruenbacher

fs/gfs2/log.c

@@ -1053,22 +1053,22 @@ void gfs2_remove_from_journal(struct buffer_head *bh, int meta)
 }
 
 /**
- * gfs2_log_flush - flush incore transaction(s)
+ * __gfs2_log_flush - flush incore transaction(s)
  * @sdp: The filesystem
  * @gl: The glock structure to flush.  If NULL, flush the whole incore log
  * @flags: The log header flags: GFS2_LOG_HEAD_FLUSH_* and debug flags
  *
  */
 
-void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
+static void __gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl,
+			     u32 flags)
 {
 	struct gfs2_trans *tr = NULL;
 	unsigned int reserved_blocks = 0, used_blocks = 0;
 	bool frozen = test_bit(SDF_FROZEN, &sdp->sd_flags);
 	unsigned int first_log_head;
 	unsigned int reserved_revokes = 0;
 
-	down_write(&sdp->sd_log_flush_lock);
 	trace_gfs2_log_flush(sdp, 1, flags);
 
 repeat:
@@ -1180,7 +1180,6 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
 		gfs2_assert_withdraw(sdp, used_blocks < reserved_blocks);
 		gfs2_log_release(sdp, reserved_blocks - used_blocks);
 	}
-	up_write(&sdp->sd_log_flush_lock);
 	gfs2_trans_free(sdp, tr);
 	trace_gfs2_log_flush(sdp, 0, flags);
 	return;
@@ -1201,6 +1200,13 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
 	goto out_end;
 }
 
+void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
+{
+	down_write(&sdp->sd_log_flush_lock);
+	__gfs2_log_flush(sdp, gl, flags);
+	up_write(&sdp->sd_log_flush_lock);
+}
+
 /**
  * gfs2_merge_trans - Merge a new transaction into a cached transaction
  * @sdp: the filesystem
@@ -1332,19 +1338,25 @@ int gfs2_logd(void *data)
 			break;
 
 		if (gfs2_jrnl_flush_reqd(sdp) || t == 0) {
+			down_write(&sdp->sd_log_flush_lock);
 			gfs2_ail1_empty(sdp, 0);
-			gfs2_log_flush(sdp, NULL, GFS2_LOG_HEAD_FLUSH_NORMAL |
-						  GFS2_LFC_LOGD_JFLUSH_REQD);
+			__gfs2_log_flush(sdp, NULL,
+					 GFS2_LOG_HEAD_FLUSH_NORMAL |
+					 GFS2_LFC_LOGD_JFLUSH_REQD);
+			up_write(&sdp->sd_log_flush_lock);
 		}
 
 		if (test_bit(SDF_FORCE_AIL_FLUSH, &sdp->sd_flags) ||
 		    gfs2_ail_flush_reqd(sdp)) {
 			clear_bit(SDF_FORCE_AIL_FLUSH, &sdp->sd_flags);
+			down_write(&sdp->sd_log_flush_lock);
 			gfs2_ail1_start(sdp);
 			gfs2_ail1_wait(sdp);
 			gfs2_ail1_empty(sdp, 0);
-			gfs2_log_flush(sdp, NULL, GFS2_LOG_HEAD_FLUSH_NORMAL |
-						  GFS2_LFC_LOGD_AIL_FLUSH_REQD);
+			__gfs2_log_flush(sdp, NULL,
+					 GFS2_LOG_HEAD_FLUSH_NORMAL |
+					 GFS2_LFC_LOGD_AIL_FLUSH_REQD);
+			up_write(&sdp->sd_log_flush_lock);
 		}
 
 		t = gfs2_tune_get(sdp, gt_logd_secs) * HZ;