windows-buf-infinite-looping-on-dirty-buffers-20090607

LICENSE MIT

If there are dirty buffers when the file server becomes unresponsive,
the cache manager will attempt to write them repeatedly resulting in
use of 100% of the cpu of the machine until the file server becomes
responsive.

This patch reduces the cpu utilization by ensuring that only the first
in a list of buffers on the same file needs to fail with timed out,
all down, all busy, all offline, or clock skew.  The other dirty buffers
will just be skipped.  A small delay is enforced in the buf_IncrSync
thread between invocation.

This patch is not a complete fix for the problem.  The buf_IncrSync
thread needs to become more intelligent in order to avoid attempts to
write to volumes that are known to be inaccessible.

diff --git a/src/WINNT/afsd/cm_buf.c b/src/WINNT/afsd/cm_buf.c
index e191bb9..245e094 100644 (file)
--- a/src/WINNT/afsd/cm_buf.c
+++ b/src/WINNT/afsd/cm_buf.c
@@ -292,7 +292,9 @@ void buf_IncrSyncer(long parm)
            i = SleepEx(5000, 1);
            if (i != 0) 
                 continue;
-       }
+       } else {
+            Sleep(50);
+        }
 
         wasDirty = buf_Sync(1);
     } /* whole daemon's while loop */
@@ -721,7 +723,14 @@ afs_uint32 buf_CleanAsyncLocked(cm_buf_t *bp, cm_req_t *reqp, afs_uint32 *pisdir
         */
        if (reqp->flags & CM_REQ_NORETRY)
            break;
-    };
+
+        /* Ditto if the hardDeadTimeout or idleTimeout was reached */
+        if (code == CM_ERROR_TIMEDOUT || code == CM_ERROR_ALLDOWN ||
+            code == CM_ERROR_ALLBUSY || code == CM_ERROR_ALLOFFLINE ||
+            code == CM_ERROR_CLOCKSKEW) {
+            break;
+        }
+    }
 
     /* if someone was waiting for the I/O that just completed or failed,
      * wake them up.
@@ -1230,7 +1239,7 @@ long buf_CountFreeList(void)
 }
 
 /* clean a buffer synchronously */
-long buf_CleanAsync(cm_buf_t *bp, cm_req_t *reqp, afs_uint32 *pisdirty)
+afs_uint32 buf_CleanAsync(cm_buf_t *bp, cm_req_t *reqp, afs_uint32 *pisdirty)
 {
     long code;
     osi_assertx(bp->magic == CM_BUF_MAGIC, "invalid cm_buf_t magic");
@@ -1728,6 +1737,15 @@ long buf_CleanVnode(struct cm_scache *scp, cm_user_t *userp, cm_req_t *reqp)
                     bp->dataVersion = CM_BUF_VERSION_BAD;
                     bp->dirtyCounter++;
                     break;
+                case CM_ERROR_TIMEDOUT:
+                case CM_ERROR_ALLDOWN:
+                case CM_ERROR_ALLBUSY:
+                case CM_ERROR_ALLOFFLINE:
+                case CM_ERROR_CLOCKSKEW:
+                    /* do not mark the buffer in error state but do
+                     * not attempt to complete the rest either.
+                     */
+                    break;
                 default:
                     code = buf_CleanAsyncLocked(bp, reqp, &wasDirty);
                     if (bp->flags & CM_BUF_ERROR) {