The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f254ac04c8744cf7bfed012717eac34eacc65dfb Mon Sep 17 00:00:00 2001

From: Jens Axboe axboe@kernel.dk Date: Wed, 12 Aug 2020 17:33:30 -0600 Subject: [PATCH] io_uring: enable lookup of links holding inflight files

When a process exits, we cancel whatever requests it has pending that are referencing the file table. However, if a link is holding a reference, then we cannot find it by simply looking at the inflight list.

Enable checking of the poll and timeout list to find the link, and cancel it appropriately.

Cc: stable@vger.kernel.org Reported-by: Josef josef.grieb@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/fs/io_uring.c b/fs/io_uring.c index 8a2afd8c33c9..1ec25ee71372 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -4937,6 +4937,7 @@ static bool io_poll_remove_one(struct io_kiocb *req) io_cqring_fill_event(req, -ECANCELED); io_commit_cqring(req->ctx); req->flags |= REQ_F_COMP_LOCKED; + req_set_fail_links(req); io_put_req(req); }

@@ -5109,6 +5110,23 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer) return HRTIMER_NORESTART; }

+static int __io_timeout_cancel(struct io_kiocb *req) +{ + int ret; + + list_del_init(&req->timeout.list); + + ret = hrtimer_try_to_cancel(&req->io->timeout.timer); + if (ret == -1) + return -EALREADY; + + req_set_fail_links(req); + req->flags |= REQ_F_COMP_LOCKED; + io_cqring_fill_event(req, -ECANCELED); + io_put_req(req); + return 0; +} + static int io_timeout_cancel(struct io_ring_ctx *ctx, __u64 user_data) { struct io_kiocb *req; @@ -5116,7 +5134,6 @@ static int io_timeout_cancel(struct io_ring_ctx *ctx, __u64 user_data)

list_for_each_entry(req, &ctx->timeout_list, timeout.list) { if (user_data == req->user_data) { - list_del_init(&req->timeout.list); ret = 0; break; } @@ -5125,15 +5142,7 @@ static int io_timeout_cancel(struct io_ring_ctx *ctx, __u64 user_data) if (ret == -ENOENT) return ret;

- ret = hrtimer_try_to_cancel(&req->io->timeout.timer); - if (ret == -1) - return -EALREADY; - - req_set_fail_links(req); - req->flags |= REQ_F_COMP_LOCKED; - io_cqring_fill_event(req, -ECANCELED); - io_put_req(req); - return 0; + return __io_timeout_cancel(req); }

static int io_timeout_remove_prep(struct io_kiocb *req, @@ -7935,6 +7944,71 @@ static bool io_wq_files_match(struct io_wq_work *work, void *data) return work->files == files; }

+/* + * Returns true if 'preq' is the link parent of 'req' + */ +static bool io_match_link(struct io_kiocb *preq, struct io_kiocb *req) +{ + struct io_kiocb *link; + + if (!(preq->flags & REQ_F_LINK_HEAD)) + return false; + + list_for_each_entry(link, &preq->link_list, link_list) { + if (link == req) + return true; + } + + return false; +} + +/* + * We're looking to cancel 'req' because it's holding on to our files, but + * 'req' could be a link to another request. See if it is, and cancel that + * parent request if so. + */ +static bool io_poll_remove_link(struct io_ring_ctx *ctx, struct io_kiocb *req) +{ + struct hlist_node *tmp; + struct io_kiocb *preq; + bool found = false; + int i; + + spin_lock_irq(&ctx->completion_lock); + for (i = 0; i < (1U << ctx->cancel_hash_bits); i++) { + struct hlist_head *list; + + list = &ctx->cancel_hash[i]; + hlist_for_each_entry_safe(preq, tmp, list, hash_node) { + found = io_match_link(preq, req); + if (found) { + io_poll_remove_one(preq); + break; + } + } + } + spin_unlock_irq(&ctx->completion_lock); + return found; +} + +static bool io_timeout_remove_link(struct io_ring_ctx *ctx, + struct io_kiocb *req) +{ + struct io_kiocb *preq; + bool found = false; + + spin_lock_irq(&ctx->completion_lock); + list_for_each_entry(preq, &ctx->timeout_list, timeout.list) { + found = io_match_link(preq, req); + if (found) { + __io_timeout_cancel(preq); + break; + } + } + spin_unlock_irq(&ctx->completion_lock); + return found; +} + static void io_uring_cancel_files(struct io_ring_ctx *ctx, struct files_struct *files) { @@ -7989,6 +8063,9 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx, } } else { io_wq_cancel_work(ctx->io_wq, &cancel_req->work); + /* could be a link, check and remove if it is */ + if (!io_poll_remove_link(ctx, cancel_req)) + io_timeout_remove_link(ctx, cancel_req); io_put_req(cancel_req); }