From: Jens Axboe axboe@kernel.dk
mainline inclusion from mainline-5.5-rc1 commit 0ddf92e848ab7abf216f218ee363eb9b9650e98f category: feature bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27 CVE: NA ---------------------------
One thing that really sucks for userspace APIs is if the kernel passes back -ENOMEM/-EAGAIN for resource shortages. The application really has no idea of what to do in those cases. Should it try and reap completions? Probably a good idea. Will it solve the issue? Who knows.
This patch adds a simple fallback mechanism if we fail to allocate memory for a request. If we fail allocating memory from the slab for a request, we punt to a pre-allocated request. There's just one of these per io_ring_ctx, but the important part is if we ever return -EBUSY to the application, the applications knows that it can wait for events and make forward progress when events have completed. This is the important part.
Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Zhihao Cheng chengzhihao1@huawei.com Signed-off-by: yangerkun yangerkun@huawei.com Reviewed-by: zhangyi (F) yi.zhang@huawei.com Signed-off-by: Cheng Jian cj.chengjian@huawei.com --- fs/io_uring.c | 46 ++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 40 insertions(+), 6 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c index 1a82dd6ddfd5..0cbe02ace776 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -239,6 +239,9 @@ struct io_ring_ctx { /* 0 is for ctx quiesce/reinit/free, 1 is for sqo_thread started */ struct completion *completions;
+ /* if all else fails... */ + struct io_kiocb *fallback_req; + #if defined(CONFIG_UNIX) struct socket *ring_sock; #endif @@ -408,6 +411,10 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p) if (!ctx) return NULL;
+ ctx->fallback_req = kmem_cache_alloc(req_cachep, GFP_KERNEL); + if (!ctx->fallback_req) + goto err; + ctx->completions = kmalloc(2 * sizeof(struct completion), GFP_KERNEL); if (!ctx->completions) goto err; @@ -432,6 +439,8 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p) INIT_LIST_HEAD(&ctx->inflight_list); return ctx; err: + if (ctx->fallback_req) + kmem_cache_free(req_cachep, ctx->fallback_req); kfree(ctx->completions); kfree(ctx); return NULL; @@ -711,6 +720,23 @@ static void io_cqring_add_event(struct io_kiocb *req, long res) io_cqring_ev_posted(ctx); }
+static inline bool io_is_fallback_req(struct io_kiocb *req) +{ + return req == (struct io_kiocb *) + ((unsigned long) req->ctx->fallback_req & ~1UL); +} + +static struct io_kiocb *io_get_fallback_req(struct io_ring_ctx *ctx) +{ + struct io_kiocb *req; + + req = ctx->fallback_req; + if (!test_and_set_bit_lock(0, (unsigned long *) ctx->fallback_req)) + return req; + + return NULL; +} + static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx, struct io_submit_state *state) { @@ -723,7 +749,7 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx, if (!state) { req = kmem_cache_alloc(req_cachep, gfp); if (unlikely(!req)) - goto out; + goto fallback; } else if (!state->free_reqs) { size_t sz; int ret; @@ -738,7 +764,7 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx, if (unlikely(ret <= 0)) { state->reqs[0] = kmem_cache_alloc(req_cachep, gfp); if (!state->reqs[0]) - goto out; + goto fallback; ret = 1; } state->free_reqs = ret - 1; @@ -750,6 +776,7 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx, state->cur_req++; }
+got_it: req->file = NULL; req->ctx = ctx; req->flags = 0; @@ -758,7 +785,10 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx, req->result = 0; INIT_IO_WORK(&req->work, io_wq_submit_work); return req; -out: +fallback: + req = io_get_fallback_req(ctx); + if (req) + goto got_it; percpu_ref_put(&ctx->refs); return NULL; } @@ -788,7 +818,10 @@ static void __io_free_req(struct io_kiocb *req) spin_unlock_irqrestore(&ctx->inflight_lock, flags); } percpu_ref_put(&ctx->refs); - kmem_cache_free(req_cachep, req); + if (likely(!io_is_fallback_req(req))) + kmem_cache_free(req_cachep, req); + else + clear_bit_unlock(0, (unsigned long *) ctx->fallback_req); }
static bool io_link_cancel_timeout(struct io_kiocb *req) @@ -1004,8 +1037,8 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events, * completions for those, only batch free for fixed * file and non-linked commands. */ - if ((req->flags & (REQ_F_FIXED_FILE|REQ_F_LINK)) == - REQ_F_FIXED_FILE) { + if (((req->flags & (REQ_F_FIXED_FILE|REQ_F_LINK)) == + REQ_F_FIXED_FILE) && !io_is_fallback_req(req)) { reqs[to_free++] = req; if (to_free == ARRAY_SIZE(reqs)) io_free_req_many(ctx, reqs, &to_free); @@ -4129,6 +4162,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx) ring_pages(ctx->sq_entries, ctx->cq_entries)); free_uid(ctx->user); kfree(ctx->completions); + kmem_cache_free(req_cachep, ctx->fallback_req); kfree(ctx); }