io_uring: retry bulk slab allocs as single allocs

I've seen cases where bulk alloc fails, since the bulk alloc API
is all-or-nothing - either we get the number we ask for, or it
returns 0 as number of entries.

If we fail a batch bulk alloc, retry a "normal" kmem_cache_alloc()
and just use that instead of failing with -EAGAIN.

While in there, ensure we use GFP_KERNEL. That was an oversight in
the original code, when we switched away from GFP_ATOMIC.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 12bb238..4c6a5e6 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -399,13 +399,14 @@ static void io_ring_drop_ctx_refs(struct io_ring_ctx *ctx, unsigned refs)
 static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
                                   struct io_submit_state *state)
 {
+       gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
        struct io_kiocb *req;
 
        if (!percpu_ref_tryget(&ctx->refs))
                return NULL;
 
        if (!state) {
-               req = kmem_cache_alloc(req_cachep, __GFP_NOWARN);
+               req = kmem_cache_alloc(req_cachep, gfp);
                if (unlikely(!req))
                        goto out;
        } else if (!state->free_reqs) {
@@ -413,10 +414,18 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
                int ret;
 
                sz = min_t(size_t, state->ios_left, ARRAY_SIZE(state->reqs));
-               ret = kmem_cache_alloc_bulk(req_cachep, __GFP_NOWARN, sz,
-                                               state->reqs);
-               if (unlikely(ret <= 0))
-                       goto out;
+               ret = kmem_cache_alloc_bulk(req_cachep, gfp, sz, state->reqs);
+
+               /*
+                * Bulk alloc is all-or-nothing. If we fail to get a batch,
+                * retry single alloc to be on the safe side.
+                */
+               if (unlikely(ret <= 0)) {
+                       state->reqs[0] = kmem_cache_alloc(req_cachep, gfp);
+                       if (!state->reqs[0])
+                               goto out;
+                       ret = 1;
+               }
                state->free_reqs = ret - 1;
                state->cur_req = 1;
                req = state->reqs[0];