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 --- scripts/livepatch/fix-patch-lines | 79 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+) create mode 100755 scripts/livepatch/fix-patch-lines (limited to 'scripts/livepatch/fix-patch-lines') diff --git a/scripts/livepatch/fix-patch-lines b/scripts/livepatch/fix-patch-lines new file mode 100755 index 000000000..fa7d4f659 --- /dev/null +++ b/scripts/livepatch/fix-patch-lines @@ -0,0 +1,79 @@ +#!/usr/bin/awk -f +# SPDX-License-Identifier: GPL-2.0 +# +# Use #line directives to preserve original __LINE__ numbers across patches to +# avoid unwanted compilation changes. + +BEGIN { + in_hunk = 0 + skip = 0 +} + +/^--- / { + skip = $2 !~ /\.(c|h)$/ + print + next +} + +/^@@/ { + if (skip) { + print + next + } + + in_hunk = 1 + + # @@ -1,3 +1,4 @@: + # 1: line number in old file + # 3: how many lines the hunk covers in old file + # 1: line number in new file + # 4: how many lines the hunk covers in new file + + match($0, /^@@ -([0-9]+)(,([0-9]+))? \+([0-9]+)(,([0-9]+))? @@/, m) + + # Set 'cur' to the old file's line number at the start of the hunk. It + # gets incremented for every context line and every line removal, so + # that it always represents the old file's current line number. + cur = m[1] + + # last = last line number of current hunk + last = cur + (m[3] ? m[3] : 1) - 1 + + need_line_directive = 0 + + print + next +} + +{ + if (skip || !in_hunk || $0 ~ /^\\ No newline at end of file/) { + print + next + } + + # change line + if ($0 ~ /^[+-]/) { + # inject #line after this group of changes + need_line_directive = 1 + + if ($0 ~ /^-/) + cur++ + + print + next + } + + # If this is the first context line after a group of changes, inject + # the #line directive to force the compiler to correct the line + # numbering to match the original file. + if (need_line_directive) { + print "+#line " cur + need_line_directive = 0 + } + + if (cur == last) + in_hunk = 0 + + cur++ + print +} -- cgit v1.3.1