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/nfs/getroot.c | 133 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 133 insertions(+) create mode 100644 fs/nfs/getroot.c (limited to 'fs/nfs/getroot.c') diff --git a/fs/nfs/getroot.c b/fs/nfs/getroot.c new file mode 100644 index 000000000..ff7424bc4 --- /dev/null +++ b/fs/nfs/getroot.c @@ -0,0 +1,133 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* getroot.c: get the root dentry for an NFS mount + * + * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + */ + +#include +#include + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include + +#include "internal.h" + +#define NFSDBG_FACILITY NFSDBG_CLIENT + +/* + * get a root dentry from the root filehandle + */ +int nfs_get_root(struct super_block *s, struct fs_context *fc) +{ + struct nfs_fs_context *ctx = nfs_fc2context(fc); + struct nfs_server *server = NFS_SB(s), *clone_server; + struct nfs_fsinfo fsinfo; + struct dentry *root; + struct inode *inode; + char *name; + int error = -ENOMEM; + unsigned long kflags = 0, kflags_out = 0; + + name = kstrdup(fc->source, GFP_KERNEL); + if (!name) + goto out; + + /* get the actual root for this mount */ + fsinfo.fattr = nfs_alloc_fattr_with_label(server); + if (fsinfo.fattr == NULL) + goto out_name; + + error = server->nfs_client->rpc_ops->getroot(server, ctx->mntfh, &fsinfo); + if (error < 0) { + dprintk("nfs_get_root: getattr error = %d\n", -error); + nfs_errorf(fc, "NFS: Couldn't getattr on root"); + goto out_fattr; + } + + inode = nfs_fhget(s, ctx->mntfh, fsinfo.fattr); + if (IS_ERR(inode)) { + dprintk("nfs_get_root: get root inode failed\n"); + error = PTR_ERR(inode); + nfs_errorf(fc, "NFS: Couldn't get root inode"); + goto out_fattr; + } + + /* root dentries normally start off anonymous and get spliced in later + * if the dentry tree reaches them; however if the dentry already + * exists, we'll pick it up at this point and use it as the root + */ + root = d_obtain_root(inode); + if (IS_ERR(root)) { + dprintk("nfs_get_root: get root dentry failed\n"); + error = PTR_ERR(root); + nfs_errorf(fc, "NFS: Couldn't get root dentry"); + goto out_fattr; + } + + security_d_instantiate(root, inode); + spin_lock(&root->d_lock); + if (IS_ROOT(root) && !root->d_fsdata && + !(root->d_flags & DCACHE_NFSFS_RENAMED)) { + root->d_fsdata = name; + name = NULL; + } + spin_unlock(&root->d_lock); + if (!s->s_root) + s->s_root = dget(root); + fc->root = root; + if (server->caps & NFS_CAP_SECURITY_LABEL) + kflags |= SECURITY_LSM_NATIVE_LABELS; + if (ctx->clone_data.sb) { + if (d_inode(fc->root)->i_fop != &nfs_dir_operations) { + error = -ESTALE; + goto error_splat_root; + } + /* clone lsm security options from the parent to the new sb */ + error = security_sb_clone_mnt_opts(ctx->clone_data.sb, + s, kflags, &kflags_out); + if (error) + goto error_splat_root; + clone_server = NFS_SB(ctx->clone_data.sb); + server->has_sec_mnt_opts = clone_server->has_sec_mnt_opts; + } else { + error = security_sb_set_mnt_opts(s, fc->security, + kflags, &kflags_out); + } + if (error) + goto error_splat_root; + if (server->caps & NFS_CAP_SECURITY_LABEL && + !(kflags_out & SECURITY_LSM_NATIVE_LABELS)) + server->caps &= ~NFS_CAP_SECURITY_LABEL; + + nfs_setsecurity(inode, fsinfo.fattr); + error = 0; + +out_fattr: + nfs_free_fattr(fsinfo.fattr); +out_name: + kfree(name); +out: + return error; +error_splat_root: + dput(fc->root); + fc->root = NULL; + goto out_fattr; +} -- cgit v1.3.1