From 89edbdfc5d0308cef57b71359331de5c4ddbf763 Mon Sep 17 00:00:00 2001 From: Mykyta Yatsenko Date: Sun, 7 Jun 2026 13:30:41 -0700 Subject: [PATCH 1/3] bpf: Fix NMI/tracepoint re-entry deadlock on lru locks NMI and tracepoint BPF programs can re-enter the per-CPU or global LRU lock that bpf_lru_pop_free()/push_free() already hold on the same CPU, AA-deadlocking. Lockdep reports "inconsistent {INITIAL USE} -> {IN-NMI}" on &l->lock (syzbot c69a0a2c816716f1e0d5) and "possible recursive locking detected" on &loc_l->lock (syzbot 18b26edb69b2e19f3b33). Prior trylock and rqspinlock based fixes (see links) were nacked because compromised on reliability. This patch converts every LRU lock site to rqspinlock_t and adds a recovery path for some failure windows to avoid node leaks. Failure recovery: - *_pop_free top-level: return NULL; prealloc_lru_pop() already treats that as no-free-element (-ENOMEM). - Cross-CPU steal: skip the victim's locked loc_l, try next CPU. - Post-steal local lock fail: publish stolen node to lockless per-CPU free_llist; next pop on this CPU picks it up. - push_free fail: mark node pending_free=1. __local_list_flush(), __local_list_pop_pending() reclaim the node from pending_list. __bpf_lru_list_shrink_inactive() reclaims the node from inactive list. Nodes from active list are reclaimed by __bpf_lru_list_shrink() or after __bpf_lru_list_rotate_active() demotes it to the inactive. Fixes: 3a08c2fd7634 ("bpf: LRU List") Reported-by: syzbot+c69a0a2c816716f1e0d5@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=c69a0a2c816716f1e0d5 Reported-by: syzbot+18b26edb69b2e19f3b33@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=18b26edb69b2e19f3b33 Link: https://lore.kernel.org/bpf/CAPPBnEYO4R+m+SpVc2gNj_x31R6fo1uJvj2bK2YS1P09GWT6kQ@mail.gmail.com/ Link: https://lore.kernel.org/bpf/CAPPBnEZmFA3ab8Uc=PEm0bdojZy=7T_F5_+eyZSHyZR3MBG4Vw@mail.gmail.com/ Link: https://lore.kernel.org/bpf/20251030030010.95352-1-dongml2@chinatelecom.cn/ Link: https://lore.kernel.org/bpf/20260119142120.28170-1-leon.hwang@linux.dev/ Signed-off-by: Mykyta Yatsenko Link: https://lore.kernel.org/r/20260607-lru_map_spin-v3-1-bcd9332e911b@meta.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/bpf_lru_list.c | 165 +++++++++++++++++++++++--------------- kernel/bpf/bpf_lru_list.h | 25 ++++-- 2 files changed, 119 insertions(+), 71 deletions(-) diff --git a/kernel/bpf/bpf_lru_list.c b/kernel/bpf/bpf_lru_list.c index e7a2fc60523f..5ed7cb4b98c0 100644 --- a/kernel/bpf/bpf_lru_list.c +++ b/kernel/bpf/bpf_lru_list.c @@ -13,23 +13,8 @@ #define PERCPU_FREE_TARGET (4) #define PERCPU_NR_SCANS PERCPU_FREE_TARGET -/* Helpers to get the local list index */ -#define LOCAL_LIST_IDX(t) ((t) - BPF_LOCAL_LIST_T_OFFSET) -#define LOCAL_FREE_LIST_IDX LOCAL_LIST_IDX(BPF_LRU_LOCAL_LIST_T_FREE) -#define LOCAL_PENDING_LIST_IDX LOCAL_LIST_IDX(BPF_LRU_LOCAL_LIST_T_PENDING) #define IS_LOCAL_LIST_TYPE(t) ((t) >= BPF_LOCAL_LIST_T_OFFSET) -/* Local list helpers */ -static struct list_head *local_free_list(struct bpf_lru_locallist *loc_l) -{ - return &loc_l->lists[LOCAL_FREE_LIST_IDX]; -} - -static struct list_head *local_pending_list(struct bpf_lru_locallist *loc_l) -{ - return &loc_l->lists[LOCAL_PENDING_LIST_IDX]; -} - /* bpf_lru_node helpers */ static bool bpf_lru_node_is_ref(const struct bpf_lru_node *node) { @@ -72,6 +57,7 @@ static void __bpf_lru_node_move_to_free(struct bpf_lru_list *l, bpf_lru_list_count_dec(l, node->type); node->type = tgt_free_type; + WRITE_ONCE(node->pending_free, 0); list_move(&node->list, free_list); } @@ -87,6 +73,9 @@ static void __bpf_lru_node_move_in(struct bpf_lru_list *l, bpf_lru_list_count_inc(l, tgt_type); node->type = tgt_type; bpf_lru_node_clear_ref(node); + /* Reset pending_free only when moving to the free list */ + if (tgt_type == BPF_LRU_LIST_T_FREE) + WRITE_ONCE(node->pending_free, 0); list_move(&node->list, &l->lists[tgt_type]); } @@ -212,9 +201,11 @@ __bpf_lru_list_shrink_inactive(struct bpf_lru *lru, unsigned int i = 0; list_for_each_entry_safe_reverse(node, tmp_node, inactive, list) { - if (bpf_lru_node_is_ref(node)) { + if (bpf_lru_node_is_ref(node) && + !READ_ONCE(node->pending_free)) { __bpf_lru_node_move(l, node, BPF_LRU_LIST_T_ACTIVE); - } else if (lru->del_from_htab(lru->del_arg, node)) { + } else if (READ_ONCE(node->pending_free) || + lru->del_from_htab(lru->del_arg, node)) { __bpf_lru_node_move_to_free(l, node, free_list, tgt_free_type); if (++nshrinked == tgt_nshrink) @@ -273,7 +264,8 @@ static unsigned int __bpf_lru_list_shrink(struct bpf_lru *lru, list_for_each_entry_safe_reverse(node, tmp_node, force_shrink_list, list) { - if (lru->del_from_htab(lru->del_arg, node)) { + if (READ_ONCE(node->pending_free) || + lru->del_from_htab(lru->del_arg, node)) { __bpf_lru_node_move_to_free(l, node, free_list, tgt_free_type); return 1; @@ -290,8 +282,10 @@ static void __local_list_flush(struct bpf_lru_list *l, struct bpf_lru_node *node, *tmp_node; list_for_each_entry_safe_reverse(node, tmp_node, - local_pending_list(loc_l), list) { - if (bpf_lru_node_is_ref(node)) + &loc_l->pending_list, list) { + if (READ_ONCE(node->pending_free)) + __bpf_lru_node_move_in(l, node, BPF_LRU_LIST_T_FREE); + else if (bpf_lru_node_is_ref(node)) __bpf_lru_node_move_in(l, node, BPF_LRU_LIST_T_ACTIVE); else __bpf_lru_node_move_in(l, node, @@ -307,9 +301,12 @@ static void bpf_lru_list_push_free(struct bpf_lru_list *l, if (WARN_ON_ONCE(IS_LOCAL_LIST_TYPE(node->type))) return; - raw_spin_lock_irqsave(&l->lock, flags); + if (raw_res_spin_lock_irqsave(&l->lock, flags)) { + WRITE_ONCE(node->pending_free, 1); + return; + } __bpf_lru_node_move(l, node, BPF_LRU_LIST_T_FREE); - raw_spin_unlock_irqrestore(&l->lock, flags); + raw_res_spin_unlock_irqrestore(&l->lock, flags); } static void bpf_lru_list_pop_free_to_local(struct bpf_lru *lru, @@ -318,8 +315,10 @@ static void bpf_lru_list_pop_free_to_local(struct bpf_lru *lru, struct bpf_lru_list *l = &lru->common_lru.lru_list; struct bpf_lru_node *node, *tmp_node; unsigned int nfree = 0; + LIST_HEAD(tmp_free); - raw_spin_lock(&l->lock); + if (raw_res_spin_lock(&l->lock)) + return; __local_list_flush(l, loc_l); @@ -327,7 +326,7 @@ static void bpf_lru_list_pop_free_to_local(struct bpf_lru *lru, list_for_each_entry_safe(node, tmp_node, &l->lists[BPF_LRU_LIST_T_FREE], list) { - __bpf_lru_node_move_to_free(l, node, local_free_list(loc_l), + __bpf_lru_node_move_to_free(l, node, &tmp_free, BPF_LRU_LOCAL_LIST_T_FREE); if (++nfree == lru->target_free) break; @@ -335,10 +334,19 @@ static void bpf_lru_list_pop_free_to_local(struct bpf_lru *lru, if (nfree < lru->target_free) __bpf_lru_list_shrink(lru, l, lru->target_free - nfree, - local_free_list(loc_l), + &tmp_free, BPF_LRU_LOCAL_LIST_T_FREE); - raw_spin_unlock(&l->lock); + raw_res_spin_unlock(&l->lock); + + /* + * Transfer the harvested nodes from the temporary list_head into + * the lockless per-CPU free llist. + */ + list_for_each_entry_safe(node, tmp_node, &tmp_free, list) { + list_del(&node->list); + llist_add(&node->llist, &loc_l->free_llist); + } } static void __local_list_add_pending(struct bpf_lru *lru, @@ -350,22 +358,21 @@ static void __local_list_add_pending(struct bpf_lru *lru, *(u32 *)((void *)node + lru->hash_offset) = hash; node->cpu = cpu; node->type = BPF_LRU_LOCAL_LIST_T_PENDING; + WRITE_ONCE(node->pending_free, 0); bpf_lru_node_clear_ref(node); - list_add(&node->list, local_pending_list(loc_l)); + list_add(&node->list, &loc_l->pending_list); } static struct bpf_lru_node * __local_list_pop_free(struct bpf_lru_locallist *loc_l) { - struct bpf_lru_node *node; + struct llist_node *llnode; - node = list_first_entry_or_null(local_free_list(loc_l), - struct bpf_lru_node, - list); - if (node) - list_del(&node->list); + llnode = llist_del_first(&loc_l->free_llist); + if (!llnode) + return NULL; - return node; + return container_of(llnode, struct bpf_lru_node, llist); } static struct bpf_lru_node * @@ -376,10 +383,10 @@ __local_list_pop_pending(struct bpf_lru *lru, struct bpf_lru_locallist *loc_l) ignore_ref: /* Get from the tail (i.e. older element) of the pending list. */ - list_for_each_entry_reverse(node, local_pending_list(loc_l), - list) { + list_for_each_entry_reverse(node, &loc_l->pending_list, list) { if ((!bpf_lru_node_is_ref(node) || force) && - lru->del_from_htab(lru->del_arg, node)) { + (READ_ONCE(node->pending_free) || + lru->del_from_htab(lru->del_arg, node))) { list_del(&node->list); return node; } @@ -404,7 +411,8 @@ static struct bpf_lru_node *bpf_percpu_lru_pop_free(struct bpf_lru *lru, l = per_cpu_ptr(lru->percpu_lru, cpu); - raw_spin_lock_irqsave(&l->lock, flags); + if (raw_res_spin_lock_irqsave(&l->lock, flags)) + return NULL; __bpf_lru_list_rotate(lru, l); @@ -420,7 +428,7 @@ static struct bpf_lru_node *bpf_percpu_lru_pop_free(struct bpf_lru *lru, __bpf_lru_node_move(l, node, BPF_LRU_LIST_T_INACTIVE); } - raw_spin_unlock_irqrestore(&l->lock, flags); + raw_res_spin_unlock_irqrestore(&l->lock, flags); return node; } @@ -437,7 +445,8 @@ static struct bpf_lru_node *bpf_common_lru_pop_free(struct bpf_lru *lru, loc_l = per_cpu_ptr(clru->local_list, cpu); - raw_spin_lock_irqsave(&loc_l->lock, flags); + if (raw_res_spin_lock_irqsave(&loc_l->lock, flags)) + return NULL; node = __local_list_pop_free(loc_l); if (!node) { @@ -448,17 +457,22 @@ static struct bpf_lru_node *bpf_common_lru_pop_free(struct bpf_lru *lru, if (node) __local_list_add_pending(lru, loc_l, cpu, node, hash); - raw_spin_unlock_irqrestore(&loc_l->lock, flags); + raw_res_spin_unlock_irqrestore(&loc_l->lock, flags); if (node) return node; - /* No free nodes found from the local free list and + /* + * No free nodes found from the local free list and * the global LRU list. * * Steal from the local free/pending list of the * current CPU and remote CPU in RR. It starts * with the loc_l->next_steal CPU. + * + * Acquire the victim's lock before touching either list. On + * acquisition failure (rqspinlock AA or timeout) skip the victim + * and try the next CPU. */ first_steal = loc_l->next_steal; @@ -466,24 +480,36 @@ static struct bpf_lru_node *bpf_common_lru_pop_free(struct bpf_lru *lru, do { steal_loc_l = per_cpu_ptr(clru->local_list, steal); - raw_spin_lock_irqsave(&steal_loc_l->lock, flags); - - node = __local_list_pop_free(steal_loc_l); - if (!node) - node = __local_list_pop_pending(lru, steal_loc_l); - - raw_spin_unlock_irqrestore(&steal_loc_l->lock, flags); + if (!raw_res_spin_lock_irqsave(&steal_loc_l->lock, flags)) { + node = __local_list_pop_free(steal_loc_l); + if (!node) + node = __local_list_pop_pending(lru, steal_loc_l); + raw_res_spin_unlock_irqrestore(&steal_loc_l->lock, flags); + } steal = cpumask_next_wrap(steal, cpu_possible_mask); } while (!node && steal != first_steal); loc_l->next_steal = steal; - if (node) { - raw_spin_lock_irqsave(&loc_l->lock, flags); - __local_list_add_pending(lru, loc_l, cpu, node, hash); - raw_spin_unlock_irqrestore(&loc_l->lock, flags); + if (!node) + return NULL; + + if (raw_res_spin_lock_irqsave(&loc_l->lock, flags)) { + /* + * The local pending lock can't be acquired (rqspinlock AA + * or timeout). Return the stolen node to the per-CPU + * free_llist instead of orphaning it; the next pop_free on + * this CPU will pick it up. + */ + node->type = BPF_LRU_LOCAL_LIST_T_FREE; + bpf_lru_node_clear_ref(node); + WRITE_ONCE(node->pending_free, 0); + llist_add(&node->llist, &loc_l->free_llist); + return NULL; } + __local_list_add_pending(lru, loc_l, cpu, node, hash); + raw_res_spin_unlock_irqrestore(&loc_l->lock, flags); return node; } @@ -511,18 +537,24 @@ static void bpf_common_lru_push_free(struct bpf_lru *lru, loc_l = per_cpu_ptr(lru->common_lru.local_list, node->cpu); - raw_spin_lock_irqsave(&loc_l->lock, flags); + if (raw_res_spin_lock_irqsave(&loc_l->lock, flags)) { + WRITE_ONCE(node->pending_free, 1); + return; + } if (unlikely(node->type != BPF_LRU_LOCAL_LIST_T_PENDING)) { - raw_spin_unlock_irqrestore(&loc_l->lock, flags); + raw_res_spin_unlock_irqrestore(&loc_l->lock, + flags); goto check_lru_list; } node->type = BPF_LRU_LOCAL_LIST_T_FREE; bpf_lru_node_clear_ref(node); - list_move(&node->list, local_free_list(loc_l)); + list_del(&node->list); - raw_spin_unlock_irqrestore(&loc_l->lock, flags); + raw_res_spin_unlock_irqrestore(&loc_l->lock, flags); + + llist_add(&node->llist, &loc_l->free_llist); return; } @@ -538,11 +570,14 @@ static void bpf_percpu_lru_push_free(struct bpf_lru *lru, l = per_cpu_ptr(lru->percpu_lru, node->cpu); - raw_spin_lock_irqsave(&l->lock, flags); + if (raw_res_spin_lock_irqsave(&l->lock, flags)) { + WRITE_ONCE(node->pending_free, 1); + return; + } __bpf_lru_node_move(l, node, BPF_LRU_LIST_T_FREE); - raw_spin_unlock_irqrestore(&l->lock, flags); + raw_res_spin_unlock_irqrestore(&l->lock, flags); } void bpf_lru_push_free(struct bpf_lru *lru, struct bpf_lru_node *node) @@ -565,6 +600,7 @@ static void bpf_common_lru_populate(struct bpf_lru *lru, void *buf, node = (struct bpf_lru_node *)(buf + node_offset); node->type = BPF_LRU_LIST_T_FREE; + node->pending_free = 0; bpf_lru_node_clear_ref(node); list_add(&node->list, &l->lists[BPF_LRU_LIST_T_FREE]); buf += elem_size; @@ -594,6 +630,7 @@ static void bpf_percpu_lru_populate(struct bpf_lru *lru, void *buf, node = (struct bpf_lru_node *)(buf + node_offset); node->cpu = cpu; node->type = BPF_LRU_LIST_T_FREE; + node->pending_free = 0; bpf_lru_node_clear_ref(node); list_add(&node->list, &l->lists[BPF_LRU_LIST_T_FREE]); i++; @@ -618,14 +655,12 @@ void bpf_lru_populate(struct bpf_lru *lru, void *buf, u32 node_offset, static void bpf_lru_locallist_init(struct bpf_lru_locallist *loc_l, int cpu) { - int i; - - for (i = 0; i < NR_BPF_LRU_LOCAL_LIST_T; i++) - INIT_LIST_HEAD(&loc_l->lists[i]); + INIT_LIST_HEAD(&loc_l->pending_list); + init_llist_head(&loc_l->free_llist); loc_l->next_steal = cpu; - raw_spin_lock_init(&loc_l->lock); + raw_res_spin_lock_init(&loc_l->lock); } static void bpf_lru_list_init(struct bpf_lru_list *l) @@ -640,7 +675,7 @@ static void bpf_lru_list_init(struct bpf_lru_list *l) l->next_inactive_rotation = &l->lists[BPF_LRU_LIST_T_INACTIVE]; - raw_spin_lock_init(&l->lock); + raw_res_spin_lock_init(&l->lock); } int bpf_lru_init(struct bpf_lru *lru, bool percpu, u32 hash_offset, diff --git a/kernel/bpf/bpf_lru_list.h b/kernel/bpf/bpf_lru_list.h index fe2661a58ea9..8d0ee61622af 100644 --- a/kernel/bpf/bpf_lru_list.h +++ b/kernel/bpf/bpf_lru_list.h @@ -6,11 +6,11 @@ #include #include -#include +#include +#include #define NR_BPF_LRU_LIST_T (3) #define NR_BPF_LRU_LIST_COUNT (2) -#define NR_BPF_LRU_LOCAL_LIST_T (2) #define BPF_LOCAL_LIST_T_OFFSET NR_BPF_LRU_LIST_T enum bpf_lru_list_type { @@ -22,10 +22,22 @@ enum bpf_lru_list_type { }; struct bpf_lru_node { - struct list_head list; + /* + * A node is in at most one list at a time. The free path on the + * per-CPU locallist uses an llist, so share storage via a union. + */ + union { + struct list_head list; + struct llist_node llist; + }; u16 cpu; u8 type; u8 ref; + /* + * Marks nodes whose *_push_free() lock acquire failed; reclaimed + * by flush/shrink which honor the flag instead of del_from_htab(). + */ + u8 pending_free; }; struct bpf_lru_list { @@ -34,13 +46,14 @@ struct bpf_lru_list { /* The next inactive list rotation starts from here */ struct list_head *next_inactive_rotation; - raw_spinlock_t lock ____cacheline_aligned_in_smp; + rqspinlock_t lock ____cacheline_aligned_in_smp; }; struct bpf_lru_locallist { - struct list_head lists[NR_BPF_LRU_LOCAL_LIST_T]; + struct list_head pending_list; + struct llist_head free_llist; u16 next_steal; - raw_spinlock_t lock; + rqspinlock_t lock; }; struct bpf_common_lru { From 8f6802d26d96ef424fc9fc9e2e68c43b6cf0fa59 Mon Sep 17 00:00:00 2001 From: Mykyta Yatsenko Date: Sun, 7 Jun 2026 13:30:42 -0700 Subject: [PATCH 2/3] Documentation/bpf: Refresh map_lru_hash_update.dot for rqspinlock Reflect the rqspinlock conversion and orphan-recovery paths added in the previous commit: - All LRU locks are rqspinlock_t; any acquire can fail (AA or timeout). A shared "rqspinlock acquire failed" terminal collapses to the existing -ENOMEM exit. Dashed arrows from each acquire site mark the failure paths. - The per-CPU local freelist is now lockless (free_llist). - Post-steal: re-acquiring loc_l->lock to insert the stolen node into the local pending list can fail; on failure the node is published to free_llist instead of being orphaned, and the call returns -ENOMEM. - Steal-loop victim lock failure is silent: skip the victim and try the next CPU. Signed-off-by: Mykyta Yatsenko Link: https://lore.kernel.org/r/20260607-lru_map_spin-v3-2-bcd9332e911b@meta.com Signed-off-by: Alexei Starovoitov --- Documentation/bpf/map_lru_hash_update.dot | 44 +++++++++++++++++++++-- 1 file changed, 42 insertions(+), 2 deletions(-) diff --git a/Documentation/bpf/map_lru_hash_update.dot b/Documentation/bpf/map_lru_hash_update.dot index ab10058f5b79..412bc8b3b57e 100644 --- a/Documentation/bpf/map_lru_hash_update.dot +++ b/Documentation/bpf/map_lru_hash_update.dot @@ -21,10 +21,18 @@ digraph { // names that initiate the corresponding logic in kernel/bpf/bpf_lru_list.c. // Number suffixes and errno suffixes handle subsections of the corresponding // logic in the function as of the writing of this dot. + // + // All LRU locks are rqspinlock_t. Every acquire can fail (AA self-deadlock + // or contention timeout); on failure the corresponding helper returns NULL + // and the caller propagates -ENOMEM. The "rqspinlock acquire failed" + // terminal below is reached via the dashed arrows from each acquire site. + + rqspinlock_failed [shape=rectangle, + label="Any LRU rqspinlock\nacquire fails\n(AA or timeout)"] // cf. __local_list_pop_free() / bpf_percpu_lru_pop_free() local_freelist_check [shape=diamond,fillcolor=1, - label="Local freelist\nnode available?"]; + label="Local freelist\nnode available?\n(lockless free_llist)"]; use_local_node [shape=rectangle, label="Use node owned\nby this CPU"] @@ -82,6 +90,15 @@ digraph { // fn__local_list_pop_pending() } + // Post-steal: re-acquire local loc_l->lock to insert the stolen node into + // the local pending list. If the acquire fails, the stolen node is published + // to the lockless local free_llist so the next pop on this CPU picks it up + // instead of orphaning it. + post_steal_lock [shape=diamond,fillcolor=1, + label="Acquire local\nloc_l->lock\nto add pending"] + post_steal_to_free_llist [shape=rectangle, + label="Publish stolen node to\nlocal free_llist (lockless)"] + fn_bpf_lru_list_pop_free_to_local2 [shape=rectangle, label="Use node that was\nnot recently referenced"] local_freelist_check4 [shape=rectangle, @@ -97,10 +114,19 @@ digraph { fn_htab_lru_map_update_elem_ENOENT [shape=oval,label="return -ENOENT"] begin -> local_freelist_check + // The initial per-CPU lock (loc_l->lock for common, l->lock for percpu) is + // acquired before the local freelist check; rqspinlock failure here exits + // directly to -ENOMEM (no recovery needed: nothing was removed yet). + local_freelist_check -> rqspinlock_failed [style=dashed, + xlabel="acquire fails"] local_freelist_check -> use_local_node [xlabel="Y"] local_freelist_check -> common_lru_check [xlabel="N"] common_lru_check -> fn_bpf_lru_list_pop_free_to_local [xlabel="Y"] common_lru_check -> fn___bpf_lru_list_shrink_inactive [xlabel="N"] + // Global lru_list lock acquire failure in pop_free_to_local: skip refill, + // fall through to the steal path. Not ENOMEM by itself. + fn_bpf_lru_list_pop_free_to_local -> common_lru_check2 [style=dashed, + xlabel="global lru_lock\nacquire fails"] fn_bpf_lru_list_pop_free_to_local -> fn___bpf_lru_node_move_to_free fn___bpf_lru_node_move_to_free -> fn_bpf_lru_list_pop_free_to_local2 [xlabel="Y"] @@ -120,13 +146,27 @@ digraph { local_freelist_check6 -> local_freelist_check7 local_freelist_check7 -> fn_htab_lru_map_update_elem - fn_htab_lru_map_update_elem -> fn_htab_lru_map_update_elem3 [xlabel = "Y"] + // Steal-loop victim lock failure is silent: treat as "no node found here" + // and continue to next CPU; same edge as the existing "N" path. + local_freelist_check5 -> fn_htab_lru_map_update_elem2 [style=dashed, + xlabel="victim's lock\nfails: skip"] + // After a successful steal, re-acquire the local loc_l->lock. On failure + // the stolen node is published to free_llist (recovered, not orphaned) + // and the update returns -ENOMEM. + fn_htab_lru_map_update_elem -> post_steal_lock [xlabel = "Y"] + post_steal_lock -> fn_htab_lru_map_update_elem3 [xlabel = "OK"] + post_steal_lock -> post_steal_to_free_llist [style=dashed, + xlabel="loc_l->lock\nacquire fails"] + post_steal_to_free_llist -> fn_htab_lru_map_update_elem_ENOMEM fn_htab_lru_map_update_elem -> fn_htab_lru_map_update_elem2 [xlabel = "N"] fn_htab_lru_map_update_elem2 -> fn_htab_lru_map_update_elem_ENOMEM [xlabel = "Y"] fn_htab_lru_map_update_elem2 -> local_freelist_check5 [xlabel = "N"] fn_htab_lru_map_update_elem3 -> fn_htab_lru_map_update_elem4 + // Shared rqspinlock-failure terminal collapses to the same -ENOMEM exit. + rqspinlock_failed -> fn_htab_lru_map_update_elem_ENOMEM + use_local_node -> fn_htab_lru_map_update_elem4 fn_bpf_lru_list_pop_free_to_local2 -> fn_htab_lru_map_update_elem4 local_freelist_check4 -> fn_htab_lru_map_update_elem4 From 6e1e4a9d60edb0e12d373fb6f2b55d90d20a363b Mon Sep 17 00:00:00 2001 From: Mykyta Yatsenko Date: Sun, 7 Jun 2026 13:30:43 -0700 Subject: [PATCH 3/3] selftests/bpf: Stress LRU rqspinlock recovery paths Introduces stress test for bpf_lru_list that exercises lock-failures and orphan-recovery, added by the LRU rqspinlock conversion. Runs three subtests: common LRU, per-CPU LRU lists (BPF_F_NO_COMMON_LRU), and per-CPU LRU map. Each pins one userspace hammer per CPU and attaches the perf_event NMI BPF prog (update+delete mix) on every online CPU. Pre-fix, lockdep fires the "INITIAL USE -> IN-NMI" splat during stress. After stress test, drain_then_verify_capacity() drains every key and refills the lru map. A stranded node on any CPU's pool would have forced eviction of a just-inserted key on that CPU, surfacing here as a missing lookup. Marked serial_ because per-CPU pinning and high-rate HW perf events would perturb parallel tests. Signed-off-by: Mykyta Yatsenko Link: https://lore.kernel.org/r/20260607-lru_map_spin-v3-3-bcd9332e911b@meta.com Signed-off-by: Alexei Starovoitov --- .../selftests/bpf/prog_tests/lru_lock_nmi.c | 243 ++++++++++++++++++ .../selftests/bpf/progs/lru_lock_nmi.c | 33 +++ 2 files changed, 276 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/lru_lock_nmi.c create mode 100644 tools/testing/selftests/bpf/progs/lru_lock_nmi.c diff --git a/tools/testing/selftests/bpf/prog_tests/lru_lock_nmi.c b/tools/testing/selftests/bpf/prog_tests/lru_lock_nmi.c new file mode 100644 index 000000000000..60666a9ba41f --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/lru_lock_nmi.c @@ -0,0 +1,243 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Stress every LRU lock-failure and orphan-recovery. + * perf_event NMI BPF on every online CPU does + * update+delete on a small LRU map; userspace threads on every CPU do + * the same from syscall context. + */ +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include "testing_helpers.h" +#include "lru_lock_nmi.skel.h" + +#define MAP_ENTRIES 64 +#define KEY_RANGE (MAP_ENTRIES * 2) +#define STRESS_NS (500 * 1000 * 1000ULL) + +struct hammer_arg { + int map_fd; + int cpu; + __u64 deadline_ns; +}; + +struct refill_arg { + int map_fd; + int cpu; + int per_cpu_quota; + int update_errors; +}; + +/* + * Pin the calling thread to @cpu. Uses dynamically-allocated CPU sets so + * we stay correct on hosts with @cpu >= CPU_SETSIZE (default 1024). + */ +static int pin_to_cpu(int cpu) +{ + cpu_set_t *cs; + size_t cs_size; + int err; + + cs = CPU_ALLOC(cpu + 1); + if (!cs) + return -ENOMEM; + cs_size = CPU_ALLOC_SIZE(cpu + 1); + + CPU_ZERO_S(cs_size, cs); + CPU_SET_S(cpu, cs_size, cs); + err = pthread_setaffinity_np(pthread_self(), cs_size, cs); + CPU_FREE(cs); + return err; +} + +static void *hammer_thread(void *p) +{ + struct hammer_arg *a = p; + int nr_possible_cpus = libbpf_num_possible_cpus(); + __u64 val[nr_possible_cpus]; + unsigned int seed; + __u32 key; + + memset(val, 0, sizeof(val)); + pin_to_cpu(a->cpu); + + seed = (unsigned int)a->cpu ^ (unsigned int)(uintptr_t)pthread_self(); + + while (get_time_ns() < a->deadline_ns) { + bool do_update = rand_r(&seed) & 1; + + key = rand_r(&seed) % KEY_RANGE; + if (do_update) + bpf_map_update_elem(a->map_fd, &key, val, BPF_ANY); + else + bpf_map_delete_elem(a->map_fd, &key); + } + return NULL; +} + +static void *refill_thread(void *p) +{ + struct refill_arg *a = p; + int nr_possible_cpus = libbpf_num_possible_cpus(); + __u64 val[nr_possible_cpus]; + __u32 start, end, key; + + memset(val, 0, sizeof(val)); + pin_to_cpu(a->cpu); + + start = (__u32)a->cpu * (__u32)a->per_cpu_quota; + end = start + (__u32)a->per_cpu_quota; + for (key = start; key < end; key++) + if (bpf_map_update_elem(a->map_fd, &key, val, BPF_ANY)) + a->update_errors++; + return NULL; +} + +/* + * Drain the map, then refill it with each CPU inserting only its own + * quota of keys. + * After refill, lookup every key we inserted - a stranded node on any + * CPU's pool would have forced eviction. + */ +static int drain_then_verify_capacity(int map_fd, int nr_cpus) +{ + int per_cpu_quota = MAP_ENTRIES / nr_cpus; + int total = per_cpu_quota * nr_cpus; + int nr_possible_cpus = libbpf_num_possible_cpus(); + pthread_t threads[nr_cpus]; + struct refill_arg args[nr_cpus]; + __u64 val[nr_possible_cpus]; + int i, hits = 0, nthreads = 0; + __u32 key; + + memset(val, 0, sizeof(val)); + + for (key = 0; key < KEY_RANGE; key++) + bpf_map_delete_elem(map_fd, &key); + + for (i = 0; i < nr_cpus; i++) { + args[i] = (struct refill_arg){ + .map_fd = map_fd, + .cpu = i, + .per_cpu_quota = per_cpu_quota, + }; + if (pthread_create(&threads[nthreads], NULL, refill_thread, &args[i]) == 0) + nthreads++; + } + for (i = 0; i < nthreads; i++) + pthread_join(threads[i], NULL); + + for (i = 0; i < nr_cpus; i++) + if (args[i].update_errors) + return -ENOMEM; + + for (key = 0; key < (__u32)total; key++) + if (bpf_map_lookup_elem(map_fd, &key, val) == 0) + hits++; + + return hits == total ? 0 : -EIO; +} + +static void run_variant(enum bpf_map_type type, __u32 map_flags, const char *name) +{ + struct perf_event_attr attr = { + .size = sizeof(attr), + .type = PERF_TYPE_HARDWARE, + .config = PERF_COUNT_HW_CPU_CYCLES, + .freq = 1, + }; + int nr_cpus, max_cpus = 64; + struct bpf_link *links[max_cpus]; + pthread_t threads[max_cpus]; + struct hammer_arg args[max_cpus]; + struct lru_lock_nmi *skel = NULL; + int map_fd, i, err, nr_threads = 0, pmu_fd = -1; + __u64 deadline; + + nr_cpus = libbpf_num_possible_cpus(); + if (!ASSERT_GT(nr_cpus, 0, "num_cpus")) + return; + + if (nr_cpus > max_cpus) + nr_cpus = max_cpus; + + if (!test__start_subtest(name)) + return; + + memset(links, 0, sizeof(links)); + skel = lru_lock_nmi__open(); + if (!ASSERT_OK_PTR(skel, "skel_open")) + goto cleanup; + + err = bpf_map__set_type(skel->maps.lru_map, type); + if (!ASSERT_OK(err, "set_type")) + goto cleanup; + err = bpf_map__set_map_flags(skel->maps.lru_map, map_flags); + if (!ASSERT_OK(err, "set_flags")) + goto cleanup; + err = bpf_map__set_max_entries(skel->maps.lru_map, MAP_ENTRIES); + if (!ASSERT_OK(err, "set_max_entries")) + goto cleanup; + + err = lru_lock_nmi__load(skel); + if (!ASSERT_OK(err, "skel_load")) + goto cleanup; + + skel->bss->hits = 0; + map_fd = bpf_map__fd(skel->maps.lru_map); + attr.sample_freq = read_perf_max_sample_freq(); + + for (i = 0; i < nr_cpus; i++) { + pmu_fd = syscall(__NR_perf_event_open, &attr, -1, i, -1, 0); + if (pmu_fd < 0) { + if (i == 0 && + (errno == ENOENT || errno == EOPNOTSUPP)) { + test__skip(); + goto cleanup; + } + continue; + } + /* libbpf takes ownership of pfd on success */ + links[i] = bpf_program__attach_perf_event(skel->progs.oncpu, pmu_fd); + if (!links[i]) + close(pmu_fd); + } + + deadline = get_time_ns() + STRESS_NS; + for (i = 0; i < nr_cpus; i++) { + args[i].map_fd = map_fd; + args[i].cpu = i; + args[i].deadline_ns = deadline; + if (pthread_create(&threads[nr_threads], NULL, hammer_thread, &args[i]) == 0) + nr_threads++; + } + for (i = 0; i < nr_threads; i++) + pthread_join(threads[i], NULL); + + for (i = 0; i < nr_cpus; i++) { + if (links[i]) { + bpf_link__destroy(links[i]); + links[i] = NULL; + } + } + + ASSERT_GT(skel->bss->hits, 0, "nmi_bpf_ran"); + ASSERT_OK(drain_then_verify_capacity(map_fd, nr_cpus), "drain_then_verify_capacity"); + +cleanup: + for (i = 0; i < nr_cpus; i++) { + if (links[i]) + bpf_link__destroy(links[i]); + } + lru_lock_nmi__destroy(skel); +} + +void serial_test_lru_lock_nmi(void) +{ + run_variant(BPF_MAP_TYPE_LRU_HASH, 0, "common_lru"); + run_variant(BPF_MAP_TYPE_LRU_HASH, BPF_F_NO_COMMON_LRU, "no_common_lru"); + run_variant(BPF_MAP_TYPE_LRU_PERCPU_HASH, 0, "percpu_lru"); +} diff --git a/tools/testing/selftests/bpf/progs/lru_lock_nmi.c b/tools/testing/selftests/bpf/progs/lru_lock_nmi.c new file mode 100644 index 000000000000..c0692cd54237 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/lru_lock_nmi.c @@ -0,0 +1,33 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include + +struct { + __uint(type, BPF_MAP_TYPE_LRU_HASH); + __uint(max_entries, 64); + __type(key, __u32); + __type(value, __u64); +} lru_map SEC(".maps"); + +int hits; + +SEC("perf_event") +int oncpu(void *ctx) +{ + /* + * Key range deliberately wider than max_entries to force LRU + * eviction on every other update. + */ + __u32 key = bpf_get_prandom_u32() % 128; + bool do_update = bpf_get_prandom_u32() & 1; + __u64 val = 1; + + if (do_update) + bpf_map_update_elem(&lru_map, &key, &val, BPF_ANY); + else + bpf_map_delete_elem(&lru_map, &key); + __sync_fetch_and_add(&hits, 1); + return 0; +} + +char _license[] SEC("license") = "GPL";