}
EXPORT_SYMBOL(bio_reset);
+static void bio_alloc_rescue(struct work_struct *work)
+{
+ struct bio_set *bs = container_of(work, struct bio_set, rescue_work);
+ struct bio *bio;
+
+ while (1) {
+ spin_lock(&bs->rescue_lock);
+ bio = bio_list_pop(&bs->rescue_list);
+ spin_unlock(&bs->rescue_lock);
+
+ if (!bio)
+ break;
+
+ generic_make_request(bio);
+ }
+}
+
+static void punt_bios_to_rescuer(struct bio_set *bs)
+{
+ struct bio_list punt, nopunt;
+ struct bio *bio;
+
+ /*
+ * In order to guarantee forward progress we must punt only bios that
+ * were allocated from this bio_set; otherwise, if there was a bio on
+ * there for a stacking driver higher up in the stack, processing it
+ * could require allocating bios from this bio_set, and doing that from
+ * our own rescuer would be bad.
+ *
+ * Since bio lists are singly linked, pop them all instead of trying to
+ * remove from the middle of the list:
+ */
+
+ bio_list_init(&punt);
+ bio_list_init(&nopunt);
+
+ while ((bio = bio_list_pop(current->bio_list)))
+ bio_list_add(bio->bi_pool == bs ? &punt : &nopunt, bio);
+
+ *current->bio_list = nopunt;
+
+ spin_lock(&bs->rescue_lock);
+ bio_list_merge(&bs->rescue_list, &punt);
+ spin_unlock(&bs->rescue_lock);
+
+ queue_work(bs->rescue_workqueue, &bs->rescue_work);
+}
+
/**
* bio_alloc_bioset - allocate a bio for I/O
* @gfp_mask: the GFP_ mask given to the slab allocator
* previously allocated bio for IO before attempting to allocate a new one.
* Failure to do so can cause deadlocks under memory pressure.
*
+ * Note that when running under generic_make_request() (i.e. any block
+ * driver), bios are not submitted until after you return - see the code in
+ * generic_make_request() that converts recursion into iteration, to prevent
+ * stack overflows.
+ *
+ * This would normally mean allocating multiple bios under
+ * generic_make_request() would be susceptible to deadlocks, but we have
+ * deadlock avoidance code that resubmits any blocked bios from a rescuer
+ * thread.
+ *
+ * However, we do not guarantee forward progress for allocations from other
+ * mempools. Doing multiple allocations from the same mempool under
+ * generic_make_request() should be avoided - instead, use bio_set's front_pad
+ * for per bio allocations.
+ *
* RETURNS:
* Pointer to new bio on success, NULL on failure.
*/
struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
{
+ gfp_t saved_gfp = gfp_mask;
unsigned front_pad;
unsigned inline_vecs;
unsigned long idx = BIO_POOL_NONE;
front_pad = 0;
inline_vecs = nr_iovecs;
} else {
+ /*
+ * generic_make_request() converts recursion to iteration; this
+ * means if we're running beneath it, any bios we allocate and
+ * submit will not be submitted (and thus freed) until after we
+ * return.
+ *
+ * This exposes us to a potential deadlock if we allocate
+ * multiple bios from the same bio_set() while running
+ * underneath generic_make_request(). If we were to allocate
+ * multiple bios (say a stacking block driver that was splitting
+ * bios), we would deadlock if we exhausted the mempool's
+ * reserve.
+ *
+ * We solve this, and guarantee forward progress, with a rescuer
+ * workqueue per bio_set. If we go to allocate and there are
+ * bios on current->bio_list, we first try the allocation
+ * without __GFP_WAIT; if that fails, we punt those bios we
+ * would be blocking to the rescuer workqueue before we retry
+ * with the original gfp_flags.
+ */
+
+ if (current->bio_list && !bio_list_empty(current->bio_list))
+ gfp_mask &= ~__GFP_WAIT;
+
p = mempool_alloc(bs->bio_pool, gfp_mask);
+ if (!p && gfp_mask != saved_gfp) {
+ punt_bios_to_rescuer(bs);
+ gfp_mask = saved_gfp;
+ p = mempool_alloc(bs->bio_pool, gfp_mask);
+ }
+
front_pad = bs->front_pad;
inline_vecs = BIO_INLINE_VECS;
}
if (nr_iovecs > inline_vecs) {
bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
+ if (!bvl && gfp_mask != saved_gfp) {
+ punt_bios_to_rescuer(bs);
+ gfp_mask = saved_gfp;
+ bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
+ }
+
if (unlikely(!bvl))
goto err_free;
} else if (nr_iovecs) {
void bioset_free(struct bio_set *bs)
{
+ if (bs->rescue_workqueue)
+ destroy_workqueue(bs->rescue_workqueue);
+
if (bs->bio_pool)
mempool_destroy(bs->bio_pool);
bs->front_pad = front_pad;
+ spin_lock_init(&bs->rescue_lock);
+ bio_list_init(&bs->rescue_list);
+ INIT_WORK(&bs->rescue_work, bio_alloc_rescue);
+
bs->bio_slab = bio_find_or_create_slab(front_pad + back_pad);
if (!bs->bio_slab) {
kfree(bs);
if (!bs->bio_pool)
goto bad;
- if (!biovec_create_pools(bs, pool_size))
- return bs;
+ if (biovec_create_pools(bs, pool_size))
+ goto bad;
+
+ bs->rescue_workqueue = alloc_workqueue("bioset", WQ_MEM_RECLAIM, 0);
+ if (!bs->rescue_workqueue)
+ goto bad;
+ return bs;
bad:
bioset_free(bs);
return NULL;
projects / mirror_ubuntu-zesty-kernel.git / blobdiff