From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- io_uring/notif.h | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) create mode 100644 io_uring/notif.h (limited to 'io_uring/notif.h') diff --git a/io_uring/notif.h b/io_uring/notif.h new file mode 100644 index 000000000..f3589cfef --- /dev/null +++ b/io_uring/notif.h @@ -0,0 +1,57 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include +#include + +#include "rsrc.h" + +#define IO_NOTIF_UBUF_FLAGS (SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN) +#define IO_NOTIF_SPLICE_BATCH 32 + +struct io_notif_data { + struct file *file; + struct ubuf_info uarg; + + struct io_notif_data *next; + struct io_notif_data *head; + + unsigned account_pages; + bool zc_report; + bool zc_used; + bool zc_copied; +}; + +struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx); +void io_tx_ubuf_complete(struct sk_buff *skb, struct ubuf_info *uarg, + bool success); + +static inline struct io_notif_data *io_notif_to_data(struct io_kiocb *notif) +{ + return io_kiocb_to_cmd(notif, struct io_notif_data); +} + +static inline void io_notif_flush(struct io_kiocb *notif) + __must_hold(¬if->ctx->uring_lock) +{ + struct io_notif_data *nd = io_notif_to_data(notif); + + io_tx_ubuf_complete(NULL, &nd->uarg, true); +} + +static inline int io_notif_account_mem(struct io_kiocb *notif, unsigned len) +{ + struct io_ring_ctx *ctx = notif->ctx; + struct io_notif_data *nd = io_notif_to_data(notif); + unsigned nr_pages = (len >> PAGE_SHIFT) + 2; + int ret; + + if (ctx->user) { + ret = __io_account_mem(ctx->user, nr_pages); + if (ret) + return ret; + nd->account_pages += nr_pages; + } + return 0; +} -- cgit v1.3.1