From 595e52284d24adc376890d3fc93bdca4707d9aca Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Wed, 13 Dec 2023 08:58:15 -0700 Subject: [PATCH 1/2] io_uring/poll: don't enable lazy wake for POLLEXCLUSIVE There are a few quirks around using lazy wake for poll unconditionally, and one of them is related the EPOLLEXCLUSIVE. Those may trigger exclusive wakeups, which wake a limited number of entries in the wait queue. If that wake number is less than the number of entries someone is waiting for (and that someone is also using DEFER_TASKRUN), then we can get stuck waiting for more entries while we should be processing the ones we already got. If we're doing exclusive poll waits, flag the request as not being compatible with lazy wakeups. Reported-by: Pavel Begunkov Fixes: 6ce4a93dbb5b ("io_uring/poll: use IOU_F_TWQ_LAZY_WAKE for wakeups") Signed-off-by: Jens Axboe --- include/linux/io_uring_types.h | 3 +++ io_uring/poll.c | 20 +++++++++++++++++--- 2 files changed, 20 insertions(+), 3 deletions(-) diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h index 805bb635cdf55..239a4f68801bb 100644 --- a/include/linux/io_uring_types.h +++ b/include/linux/io_uring_types.h @@ -434,6 +434,7 @@ enum { /* keep async read/write and isreg together and in order */ REQ_F_SUPPORT_NOWAIT_BIT, REQ_F_ISREG_BIT, + REQ_F_POLL_NO_LAZY_BIT, /* not a real bit, just to check we're not overflowing the space */ __REQ_F_LAST_BIT, @@ -501,6 +502,8 @@ enum { REQ_F_CLEAR_POLLIN = BIT(REQ_F_CLEAR_POLLIN_BIT), /* hashed into ->cancel_hash_locked, protected by ->uring_lock */ REQ_F_HASH_LOCKED = BIT(REQ_F_HASH_LOCKED_BIT), + /* don't use lazy poll wake for this request */ + REQ_F_POLL_NO_LAZY = BIT(REQ_F_POLL_NO_LAZY_BIT), }; typedef void (*io_req_tw_func_t)(struct io_kiocb *req, struct io_tw_state *ts); diff --git a/io_uring/poll.c b/io_uring/poll.c index d38d05edb4fa2..d59b74a99d4e4 100644 --- a/io_uring/poll.c +++ b/io_uring/poll.c @@ -366,11 +366,16 @@ void io_poll_task_func(struct io_kiocb *req, struct io_tw_state *ts) static void __io_poll_execute(struct io_kiocb *req, int mask) { + unsigned flags = 0; + io_req_set_res(req, mask, 0); req->io_task_work.func = io_poll_task_func; trace_io_uring_task_add(req, mask); - __io_req_task_work_add(req, IOU_F_TWQ_LAZY_WAKE); + + if (!(req->flags & REQ_F_POLL_NO_LAZY)) + flags = IOU_F_TWQ_LAZY_WAKE; + __io_req_task_work_add(req, flags); } static inline void io_poll_execute(struct io_kiocb *req, int res) @@ -526,10 +531,19 @@ static void __io_queue_proc(struct io_poll *poll, struct io_poll_table *pt, poll->head = head; poll->wait.private = (void *) wqe_private; - if (poll->events & EPOLLEXCLUSIVE) + if (poll->events & EPOLLEXCLUSIVE) { + /* + * Exclusive waits may only wake a limited amount of entries + * rather than all of them, this may interfere with lazy + * wake if someone does wait(events > 1). Ensure we don't do + * lazy wake for those, as we need to process each one as they + * come in. + */ + req->flags |= REQ_F_POLL_NO_LAZY; add_wait_queue_exclusive(head, &poll->wait); - else + } else { add_wait_queue(head, &poll->wait); + } } static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head, From 1ba0e9d69b2000e95267c888cbfa91d823388d47 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Thu, 14 Dec 2023 21:34:08 +0000 Subject: [PATCH 2/2] io_uring/cmd: fix breakage in SOCKET_URING_OP_SIOC* implementation In 8e9fad0e70b7 "io_uring: Add io_uring command support for sockets" you've got an include of asm-generic/ioctls.h done in io_uring/uring_cmd.c. That had been done for the sake of this chunk - + ret = prot->ioctl(sk, SIOCINQ, &arg); + if (ret) + return ret; + return arg; + case SOCKET_URING_OP_SIOCOUTQ: + ret = prot->ioctl(sk, SIOCOUTQ, &arg); SIOC{IN,OUT}Q are defined to symbols (FIONREAD and TIOCOUTQ) that come from ioctls.h, all right, but the values vary by the architecture. FIONREAD is 0x467F on mips 0x4004667F on alpha, powerpc and sparc 0x8004667F on sh and xtensa 0x541B everywhere else TIOCOUTQ is 0x7472 on mips 0x40047473 on alpha, powerpc and sparc 0x80047473 on sh and xtensa 0x5411 everywhere else ->ioctl() expects the same values it would've gotten from userland; all places where we compare with SIOC{IN,OUT}Q are using asm/ioctls.h, so they pick the correct values. io_uring_cmd_sock(), OTOH, ends up passing the default ones. Fixes: 8e9fad0e70b7 ("io_uring: Add io_uring command support for sockets") Cc: Signed-off-by: Al Viro Link: https://lore.kernel.org/r/20231214213408.GT1674809@ZenIV Signed-off-by: Jens Axboe --- io_uring/uring_cmd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c index acbc2924ecd21..7d3ef62e620a5 100644 --- a/io_uring/uring_cmd.c +++ b/io_uring/uring_cmd.c @@ -7,7 +7,7 @@ #include #include -#include +#include #include "io_uring.h" #include "rsrc.h"