From 9fe3eaea4a3530ca34a8d8ff00b1848c528789ca Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Wed, 31 Jan 2024 10:50:08 -0700 Subject: [PATCH] io_uring: remove unconditional looping in local task_work handling If we have a ton of notifications coming in, we can be looping in here for a long time. This can be problematic for various reasons, mostly because we can starve userspace. If the application is waiting on N events, then only re-run if we need more events. Fixes: c0e0d6ba25f1 ("io_uring: add IORING_SETUP_DEFER_TASKRUN") Signed-off-by: Jens Axboe --- io_uring/io_uring.c | 44 +++++++++++++++++++++++++++++--------------- 1 file changed, 29 insertions(+), 15 deletions(-) diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 007cef9738ee..d31e8b110de9 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -1386,7 +1386,20 @@ static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx) } } -static int __io_run_local_work(struct io_ring_ctx *ctx, struct io_tw_state *ts) +static bool io_run_local_work_continue(struct io_ring_ctx *ctx, int events, + int min_events) +{ + if (llist_empty(&ctx->work_llist)) + return false; + if (events < min_events) + return true; + if (ctx->flags & IORING_SETUP_TASKRUN_FLAG) + atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags); + return false; +} + +static int __io_run_local_work(struct io_ring_ctx *ctx, struct io_tw_state *ts, + int min_events) { struct llist_node *node; unsigned int loops = 0; @@ -1414,18 +1427,20 @@ again: } loops++; - if (!llist_empty(&ctx->work_llist)) + if (io_run_local_work_continue(ctx, ret, min_events)) goto again; if (ts->locked) { io_submit_flush_completions(ctx); - if (!llist_empty(&ctx->work_llist)) + if (io_run_local_work_continue(ctx, ret, min_events)) goto again; } + trace_io_uring_local_work_run(ctx, ret, loops); return ret; } -static inline int io_run_local_work_locked(struct io_ring_ctx *ctx) +static inline int io_run_local_work_locked(struct io_ring_ctx *ctx, + int min_events) { struct io_tw_state ts = { .locked = true, }; int ret; @@ -1433,20 +1448,20 @@ static inline int io_run_local_work_locked(struct io_ring_ctx *ctx) if (llist_empty(&ctx->work_llist)) return 0; - ret = __io_run_local_work(ctx, &ts); + ret = __io_run_local_work(ctx, &ts, min_events); /* shouldn't happen! */ if (WARN_ON_ONCE(!ts.locked)) mutex_lock(&ctx->uring_lock); return ret; } -static int io_run_local_work(struct io_ring_ctx *ctx) +static int io_run_local_work(struct io_ring_ctx *ctx, int min_events) { struct io_tw_state ts = {}; int ret; ts.locked = mutex_trylock(&ctx->uring_lock); - ret = __io_run_local_work(ctx, &ts); + ret = __io_run_local_work(ctx, &ts, min_events); if (ts.locked) mutex_unlock(&ctx->uring_lock); @@ -1642,7 +1657,7 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min) io_task_work_pending(ctx)) { u32 tail = ctx->cached_cq_tail; - (void) io_run_local_work_locked(ctx); + (void) io_run_local_work_locked(ctx, min); if (task_work_pending(current) || wq_list_empty(&ctx->iopoll_list)) { @@ -2486,7 +2501,7 @@ int io_run_task_work_sig(struct io_ring_ctx *ctx) { if (!llist_empty(&ctx->work_llist)) { __set_current_state(TASK_RUNNING); - if (io_run_local_work(ctx) > 0) + if (io_run_local_work(ctx, INT_MAX) > 0) return 0; } if (io_run_task_work() > 0) @@ -2554,7 +2569,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, if (!io_allowed_run_tw(ctx)) return -EEXIST; if (!llist_empty(&ctx->work_llist)) - io_run_local_work(ctx); + io_run_local_work(ctx, min_events); io_run_task_work(); io_cqring_overflow_flush(ctx); /* if user messes with these they will just get an early return */ @@ -2592,11 +2607,10 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, trace_io_uring_cqring_wait(ctx, min_events); do { + int nr_wait = (int) iowq.cq_tail - READ_ONCE(ctx->rings->cq.tail); unsigned long check_cq; if (ctx->flags & IORING_SETUP_DEFER_TASKRUN) { - int nr_wait = (int) iowq.cq_tail - READ_ONCE(ctx->rings->cq.tail); - atomic_set(&ctx->cq_wait_nr, nr_wait); set_current_state(TASK_INTERRUPTIBLE); } else { @@ -2615,7 +2629,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, */ io_run_task_work(); if (!llist_empty(&ctx->work_llist)) - io_run_local_work(ctx); + io_run_local_work(ctx, nr_wait); /* * Non-local task_work will be run on exit to userspace, but @@ -3270,7 +3284,7 @@ static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx, if ((ctx->flags & IORING_SETUP_DEFER_TASKRUN) && io_allowed_defer_tw_run(ctx)) - ret |= io_run_local_work(ctx) > 0; + ret |= io_run_local_work(ctx, INT_MAX) > 0; ret |= io_cancel_defer_files(ctx, task, cancel_all); mutex_lock(&ctx->uring_lock); ret |= io_poll_remove_all(ctx, task, cancel_all); @@ -3632,7 +3646,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit, * it should handle ownership problems if any. */ if (ctx->flags & IORING_SETUP_DEFER_TASKRUN) - (void)io_run_local_work_locked(ctx); + (void)io_run_local_work_locked(ctx, min_complete); } mutex_unlock(&ctx->uring_lock); }