FS-Cache: When submitting an op, cancel it if the target object is dying

When submitting an operation, prefer to cancel the operation immediately
rather than queuing it for later processing if the object is marked as dying
(ie. the object state machine has reached the KILL_OBJECT state).

Whilst we're at it, change the series of related test_bit() calls into a
READ_ONCE() and bitwise-AND operators to reduce the number of load
instructions (test_bit() has a volatile address).

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jeff.layton@primarydata.com>

diff --git a/fs/fscache/operation.c b/fs/fscache/operation.c
index 68ead84826178244a5141d2282f8192d63c47d4c..dec6defe3be30941bbd0171bfba560e42bd78919 100644 (file)
--- a/fs/fscache/operation.c
+++ b/fs/fscache/operation.c
@@ -120,6 +120,8 @@ static void fscache_report_unexpected_submission(struct fscache_object *object,
 int fscache_submit_exclusive_op(struct fscache_object *object,
                                struct fscache_operation *op)
 {
+       const struct fscache_state *ostate;
+       unsigned long flags;
        int ret;
 
        _enter("{OBJ%x OP%x},", object->debug_id, op->debug_id);
@@ -132,8 +134,19 @@ int fscache_submit_exclusive_op(struct fscache_object *object,
        ASSERTCMP(object->n_ops, >=, object->n_exclusive);
        ASSERT(list_empty(&op->pend_link));
 
+       ostate = object->state;
+       smp_rmb();
+
        op->state = FSCACHE_OP_ST_PENDING;
-       if (fscache_object_is_active(object)) {
+       flags = READ_ONCE(object->flags);
+       if (unlikely(!(flags & BIT(FSCACHE_OBJECT_IS_LIVE)))) {
+               fscache_stat(&fscache_n_op_rejected);
+               op->state = FSCACHE_OP_ST_CANCELLED;
+               ret = -ENOBUFS;
+       } else if (unlikely(fscache_cache_is_broken(object))) {
+               op->state = FSCACHE_OP_ST_CANCELLED;
+               ret = -EIO;
+       } else if (flags & BIT(FSCACHE_OBJECT_IS_AVAILABLE)) {
                op->object = object;
                object->n_ops++;
                object->n_exclusive++;  /* reads and writes must wait */
@@ -155,7 +168,7 @@ int fscache_submit_exclusive_op(struct fscache_object *object,
                /* need to issue a new write op after this */
                clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
                ret = 0;
-       } else if (test_bit(FSCACHE_OBJECT_IS_LOOKED_UP, &object->flags)) {
+       } else if (flags & BIT(FSCACHE_OBJECT_IS_LOOKED_UP)) {
                op->object = object;
                object->n_ops++;
                object->n_exclusive++;  /* reads and writes must wait */
@@ -164,11 +177,9 @@ int fscache_submit_exclusive_op(struct fscache_object *object,
                fscache_stat(&fscache_n_op_pend);
                ret = 0;
        } else {
-               /* If we're in any other state, there must have been an I/O
-                * error of some nature.
-                */
-               ASSERT(test_bit(FSCACHE_IOERROR, &object->cache->flags));
-               ret = -EIO;
+               fscache_report_unexpected_submission(object, op, ostate);
+               op->state = FSCACHE_OP_ST_CANCELLED;
+               ret = -ENOBUFS;
        }
 
        spin_unlock(&object->lock);
@@ -187,6 +198,7 @@ int fscache_submit_op(struct fscache_object *object,
                      struct fscache_operation *op)
 {
        const struct fscache_state *ostate;
+       unsigned long flags;
        int ret;
 
        _enter("{OBJ%x OP%x},{%u}",
@@ -204,7 +216,15 @@ int fscache_submit_op(struct fscache_object *object,
        smp_rmb();
 
        op->state = FSCACHE_OP_ST_PENDING;
-       if (fscache_object_is_active(object)) {
+       flags = READ_ONCE(object->flags);
+       if (unlikely(!(flags & BIT(FSCACHE_OBJECT_IS_LIVE)))) {
+               fscache_stat(&fscache_n_op_rejected);
+               op->state = FSCACHE_OP_ST_CANCELLED;
+               ret = -ENOBUFS;
+       } else if (unlikely(fscache_cache_is_broken(object))) {
+               op->state = FSCACHE_OP_ST_CANCELLED;
+               ret = -EIO;
+       } else if (flags & BIT(FSCACHE_OBJECT_IS_AVAILABLE)) {
                op->object = object;
                object->n_ops++;
 
@@ -222,25 +242,18 @@ int fscache_submit_op(struct fscache_object *object,
                        fscache_run_op(object, op);
                }
                ret = 0;
-       } else if (test_bit(FSCACHE_OBJECT_IS_LOOKED_UP, &object->flags)) {
+       } else if (flags & BIT(FSCACHE_OBJECT_IS_LOOKED_UP)) {
                op->object = object;
                object->n_ops++;
                atomic_inc(&op->usage);
                list_add_tail(&op->pend_link, &object->pending_ops);
                fscache_stat(&fscache_n_op_pend);
                ret = 0;
-       } else if (fscache_object_is_dying(object)) {
-               fscache_stat(&fscache_n_op_rejected);
-               op->state = FSCACHE_OP_ST_CANCELLED;
-               ret = -ENOBUFS;
-       } else if (!test_bit(FSCACHE_IOERROR, &object->cache->flags)) {
+       } else {
                fscache_report_unexpected_submission(object, op, ostate);
                ASSERT(!fscache_object_is_active(object));
                op->state = FSCACHE_OP_ST_CANCELLED;
                ret = -ENOBUFS;
-       } else {
-               op->state = FSCACHE_OP_ST_CANCELLED;
-               ret = -ENOBUFS;
        }
 
        spin_unlock(&object->lock);

diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index c9dafdaf3347d55caaa94a7ebe8c98ea3f8081c5..2e83a141e465c3e59e91a615e3c1ad2e9aa3fa35 100644 (file)
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -411,17 +411,22 @@ static inline bool fscache_object_is_available(struct fscache_object *object)
        return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
 }
 
+static inline bool fscache_cache_is_broken(struct fscache_object *object)
+{
+       return test_bit(FSCACHE_IOERROR, &object->cache->flags);
+}
+
 static inline bool fscache_object_is_active(struct fscache_object *object)
 {
        return fscache_object_is_available(object) &&
                fscache_object_is_live(object) &&
-               !test_bit(FSCACHE_IOERROR, &object->cache->flags);
+               !fscache_cache_is_broken(object);
 }
 
 static inline bool fscache_object_is_dead(struct fscache_object *object)
 {
        return fscache_object_is_dying(object) &&
-               test_bit(FSCACHE_IOERROR, &object->cache->flags);
+               fscache_cache_is_broken(object);
 }
 
 /**