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 --- fs/9p/cache.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 76 insertions(+) create mode 100644 fs/9p/cache.c (limited to 'fs/9p/cache.c') diff --git a/fs/9p/cache.c b/fs/9p/cache.c new file mode 100644 index 000000000..12c0ae29f --- /dev/null +++ b/fs/9p/cache.c @@ -0,0 +1,76 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * V9FS cache definitions. + * + * Copyright (C) 2009 by Abhishek Kulkarni + */ + +#include +#include +#include +#include +#include +#include +#include + +#include "v9fs.h" +#include "cache.h" + +int v9fs_cache_session_get_cookie(struct v9fs_session_info *v9ses, + const char *dev_name) +{ + struct fscache_volume *vcookie; + char *name, *p; + + name = kasprintf(GFP_KERNEL, "9p,%s,%s", + dev_name, v9ses->cachetag ?: v9ses->aname); + if (!name) + return -ENOMEM; + + for (p = name; *p; p++) + if (*p == '/') + *p = ';'; + + vcookie = fscache_acquire_volume(name, NULL, NULL, 0); + p9_debug(P9_DEBUG_FSC, "session %p get volume %p (%s)\n", + v9ses, vcookie, name); + if (IS_ERR(vcookie)) { + if (vcookie != ERR_PTR(-EBUSY)) { + kfree(name); + return PTR_ERR(vcookie); + } + pr_err("Cache volume key already in use (%s)\n", name); + vcookie = NULL; + } + v9ses->fscache = vcookie; + kfree(name); + return 0; +} + +void v9fs_cache_inode_get_cookie(struct inode *inode) +{ + struct v9fs_inode *v9inode = V9FS_I(inode); + struct v9fs_session_info *v9ses; + __le32 version; + __le64 path; + + if (!S_ISREG(inode->i_mode)) + return; + if (WARN_ON(v9fs_inode_cookie(v9inode))) + return; + + version = cpu_to_le32(v9inode->qid.version); + path = cpu_to_le64(v9inode->qid.path); + v9ses = v9fs_inode2v9ses(inode); + v9inode->netfs.cache = + fscache_acquire_cookie(v9fs_session_cache(v9ses), + 0, + &path, sizeof(path), + &version, sizeof(version), + i_size_read(&v9inode->netfs.inode)); + if (v9inode->netfs.cache) + mapping_set_release_always(inode->i_mapping); + + p9_debug(P9_DEBUG_FSC, "inode %p get cookie %p\n", + inode, v9fs_inode_cookie(v9inode)); +} -- cgit v1.3.1