On 12/13/24 11:11, syzbot wrote:
================================================================== BUG: KCSAN: data-race in io_recv / io_wq_free_work write to 0xffff88814248b848 of 8 bytes by task 22395 on cpu 1: io_recv+0x661/0xa70 io_issue_sqe+0x150/0xc10 io_uring/io_uring.c:1736 io_poll_issue+0x1a/0x20 io_uring/io_uring.c:1767 io_poll_check_events io_uring/poll.c:289 [inline] io_poll_task_func+0x205/0x7c0 io_uring/poll.c:316 io_handle_tw_list+0xe3/0x200 io_uring/io_uring.c:1053 tctx_task_work_run+0x6e/0x1c0 io_uring/io_uring.c:1117 tctx_task_work+0x40/0x80 io_uring/io_uring.c:1135 task_work_run+0x13a/0x1a0 kernel/task_work.c:239 io_run_task_work+0x1b1/0x200 io_uring/io_uring.h:343 io_cqring_wait io_uring/io_uring.c:2594 [inline] __do_sys_io_uring_enter io_uring/io_uring.c:3434 [inline] __se_sys_io_uring_enter+0x14f5/0x1ba0 io_uring/io_uring.c:3325 __x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:3325 x64_sys_call+0xb5e/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:427 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f read to 0xffff88814248b848 of 8 bytes by task 22396 on cpu 0: req_ref_put_and_test io_uring/refs.h:22 [inline] io_wq_free_work+0x24/0x1b0 io_uring/io_uring.c:1776 io_worker_handle_work+0x4cb/0x9d0 io_uring/io-wq.c:604 io_wq_worker+0x286/0x820 io_uring/io-wq.c:655 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 value changed: 0x0000000085584038 -> 0x0000000085184
IIUC what that it, it's known and mild. Writes to flags are synchronised, for concurrent reads we make sure the interesting bits are set in advance. i.e. only a problem if compiler decides to mask a bit while modifying an unrelated bit or so. We probably need WRITE_ONCE or splitting flags into two sets. -- Pavel Begunkov
