886d0137f1
Ran into a use-after-free on the main io-wq struct, wq. It has a worker ref and completion event, but the manager itself isn't holding a reference. This can lead to a race where the manager thinks there are no workers and exits, but a worker is being added. That leads to the following trace: BUG: KASAN: use-after-free in io_wqe_worker+0x4c0/0x5e0 Read of size 8 at addr ffff888108baa8a0 by task iou-wrk-3080422/3080425 CPU: 5 PID: 3080425 Comm: iou-wrk-3080422 Not tainted 5.12.0-rc1+ #110 Hardware name: Micro-Star International Co., Ltd. MS-7C60/TRX40 PRO 10G (MS-7C60), BIOS 1.60 05/13/2020 Call Trace: dump_stack+0x90/0xbe print_address_description.constprop.0+0x67/0x28d ? io_wqe_worker+0x4c0/0x5e0 kasan_report.cold+0x7b/0xd4 ? io_wqe_worker+0x4c0/0x5e0 __asan_load8+0x6d/0xa0 io_wqe_worker+0x4c0/0x5e0 ? io_worker_handle_work+0xc00/0xc00 ? recalc_sigpending+0xe5/0x120 ? io_worker_handle_work+0xc00/0xc00 ? io_worker_handle_work+0xc00/0xc00 ret_from_fork+0x1f/0x30 Allocated by task 3080422: kasan_save_stack+0x23/0x60 __kasan_kmalloc+0x80/0xa0 kmem_cache_alloc_node_trace+0xa0/0x480 io_wq_create+0x3b5/0x600 io_uring_alloc_task_context+0x13c/0x380 io_uring_add_task_file+0x109/0x140 __x64_sys_io_uring_enter+0x45f/0x660 do_syscall_64+0x32/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae Freed by task 3080422: kasan_save_stack+0x23/0x60 kasan_set_track+0x20/0x40 kasan_set_free_info+0x24/0x40 __kasan_slab_free+0xe8/0x120 kfree+0xa8/0x400 io_wq_put+0x14a/0x220 io_wq_put_and_exit+0x9a/0xc0 io_uring_clean_tctx+0x101/0x140 __io_uring_files_cancel+0x36e/0x3c0 do_exit+0x169/0x1340 __x64_sys_exit+0x34/0x40 do_syscall_64+0x32/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae Have the manager itself hold a reference, and now both drop points drop and complete if we hit zero, and the manager can unconditionally do a wait_for_completion() instead of having a race between reading the ref count and waiting if it was non-zero. Fixes: fb3a1f6c745c ("io-wq: have manager wait for all workers to exit") Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.