From 44575a67314b3768d4415252271e8f60c5c70118 Mon Sep 17 00:00:00 2001 From: Xiaoguang Wang Date: Sun, 19 Apr 2020 10:06:55 +0800 Subject: [PATCH] io_uring: only restore req->work for req that needs do completion When testing io_uring IORING_FEAT_FAST_POLL feature, I got below panic: BUG: kernel NULL pointer dereference, address: 0000000000000030 PGD 0 P4D 0 Oops: 0000 [#1] SMP PTI CPU: 5 PID: 2154 Comm: io_uring_echo_s Not tainted 5.6.0+ #359 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.1-0-g0551a4be2c-prebuilt.qemu-project.org 04/01/2014 RIP: 0010:io_wq_submit_work+0xf/0xa0 Code: ff ff ff be 02 00 00 00 e8 ae c9 19 00 e9 58 ff ff ff 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 54 49 89 fc 55 53 48 8b 2f <8b> 45 30 48 8d 9d 48 ff ff ff 25 01 01 00 00 83 f8 01 75 07 eb 2a RSP: 0018:ffffbef543e93d58 EFLAGS: 00010286 RAX: ffffffff84364f50 RBX: ffffa3eb50f046b8 RCX: 0000000000000000 RDX: ffffa3eb0efc1840 RSI: 0000000000000006 RDI: ffffa3eb50f046b8 RBP: 0000000000000000 R08: 00000000fffd070d R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffffa3eb50f046b8 R13: ffffa3eb0efc2088 R14: ffffffff85b69be0 R15: ffffa3eb0effa4b8 FS: 00007fe9f69cc4c0(0000) GS:ffffa3eb5ef40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000030 CR3: 0000000020410000 CR4: 00000000000006e0 Call Trace: task_work_run+0x6d/0xa0 do_exit+0x39a/0xb80 ? get_signal+0xfe/0xbc0 do_group_exit+0x47/0xb0 get_signal+0x14b/0xbc0 ? __x64_sys_io_uring_enter+0x1b7/0x450 do_signal+0x2c/0x260 ? __x64_sys_io_uring_enter+0x228/0x450 exit_to_usermode_loop+0x87/0xf0 do_syscall_64+0x209/0x230 entry_SYSCALL_64_after_hwframe+0x49/0xb3 RIP: 0033:0x7fe9f64f8df9 Code: Bad RIP value. task_work_run calls io_wq_submit_work unexpectedly, it's obvious that struct callback_head's func member has been changed. After looking into codes, I found this issue is still due to the union definition: union { /* * Only commands that never go async can use the below fields, * obviously. Right now only IORING_OP_POLL_ADD uses them, and * async armed poll handlers for regular commands. The latter * restore the work, if needed. */ struct { struct callback_head task_work; struct hlist_node hash_node; struct async_poll *apoll; }; struct io_wq_work work; }; When task_work_run has multiple work to execute, the work that calls io_poll_remove_all() will do req->work restore for non-poll request always, but indeed if a non-poll request has been added to a new callback_head, subsequent callback will call io_async_task_func() to handle this request, that means we should not do the restore work for such non-poll request. Meanwhile in io_async_task_func(), we should drop submit ref when req has been canceled. Fix both issues. Fixes: b1f573bd15fd ("io_uring: restore req->work when canceling poll request") Signed-off-by: Xiaoguang Wang Use io_double_put_req() Signed-off-by: Jens Axboe --- fs/io_uring.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 381d50becd04..c687f57fb651 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -4200,17 +4200,17 @@ static void io_async_task_func(struct callback_head *cb) spin_unlock_irq(&ctx->completion_lock); + /* restore ->work in case we need to retry again */ + memcpy(&req->work, &apoll->work, sizeof(req->work)); + if (canceled) { kfree(apoll); io_cqring_ev_posted(ctx); req_set_fail_links(req); - io_put_req(req); + io_double_put_req(req); return; } - /* restore ->work in case we need to retry again */ - memcpy(&req->work, &apoll->work, sizeof(req->work)); - __set_current_state(TASK_RUNNING); mutex_lock(&ctx->uring_lock); __io_queue_sqe(req, NULL); @@ -4369,7 +4369,7 @@ static bool io_poll_remove_one(struct io_kiocb *req) hash_del(&req->hash_node); - if (apoll) { + if (do_complete && apoll) { /* * restore ->work because we need to call io_req_work_drop_env. */