From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793621765; b=nD9JiiDhGrqWigoOd1EwZ74UhyUYX9jwLA05vypTPKWytglowV1jttkc7RaPdtP/m4p8 /iApGJnX9+TbP7CCXdF5TdWEpkSbB8AD1DsvIW0CJ4q6VV0ovyGpexPyR6VLWKf232NSl 6HAqvvyxNNInzXf9tJXvmeHpVB6jxd7lN2P+TGprjfXNYNGZdDlAI+ivyUXa+TPtoVDh/ 9x3OYdsgre4Qqda6MXWFm4fNVWCObdz6IyXnbkg3Z8cL+VD+WSXPV4AHWLFMLLV8LpkDM 0016+4mf6gzAjfS+fpBp4ysRTtZsNT52D19akSH3RIK7FGFbETQOyyzqlf7n8tyhyoA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793621765; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=WpLDsRwimu47hyRRLvXEi3CARIG877KZeTYZ+fUXXTM=; b=r/UvkqqDXAeYNHD2vDCsGk/EuK1hJYfAKwSQN9dCVHNJ2e+f9Gsdh4t7vR4NWHyewDvC mp81FndesLXpSH19v8J9YJ0oy3mfKwT+vaWAZWSELD0MyKL6FbzJY2PA1y+At/hfYC4Sq jXZPgsJUgrHtZa09kDhNHhKEpdDox4QdaVl/2U2zbvVJJch2EmWbFZ0ATubYaYbRFwZae OVzkJ9cOblrqPwQU+LLv5e415YTBYngXRqeIw7qZCWwUCrzJJsLLp+v8/R69HjbKB9FKg eYB2KHwL3lZGu5h6V0I70BkLfDR9LzqshpFTo0g0SbD3bQwoPivpFXwm7MonLQ3dnQQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=RBIHs1WY; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with UTF8SMTPS id E8210606A85F; Mon, 2 Nov 2026 12:16:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=RBIHs1WY Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 0F91C1F0180D; Mon, 2 Nov 2026 12:16:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793621764; bh=WpLDsRwimu47hyRRLvXEi3CARIG877KZeTYZ+fUXXTM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=RBIHs1WYf1dV70X/rIm5tCjVH7kgVYJuWKf9jayesFHGELiHhgJllfKeoMgXpdgRO Nrahr5+azRbZW8AbAlcpc4e4j+tLUX6ge+HjbCaRh8f3GNogvwHj0gHmwmxsR4AP8U Xw8LTB8j+vGVscGhMQ6HympVHD/BWAdhsyLfGDMlq2PJF8EkGfsWzuRCvzEkVBRhOy aN19Op4QmA2ImUc0SwPtnOexu4jgQhS86d0gSKXhpMLT7gbTfer6ma4tMUBn87RBly 7Z5VaSgxh84hTxdmg6sQb012KV5XL1c05vlgR4h4OC8n3kBOsILFrAOuFttjrou1CD sFYSvhLLAsqYg== From: Jarkko Sakkinen To: David Howells Cc: Eric Biggers , linux-integrity@vger.kernel.org, Mimi Zohar , Jarkko Sakkinen , Roberto Sassu , Dmitry Kasatkin , Eric Snowberg , Paul Moore , James Morris , "Serge E. Hallyn" , linux-security-module@vger.kernel.org (open list:SECURITY SUBSYSTEM), linux-kernel@vger.kernel.org (open list), keyrings@vger.kernel.org (open list:KEYS/KEYRINGS) Subject: [RFC PATCH 4/4] KEYS: key_garbage_collector(): process in chunks Date: Mon, 2 Nov 2026 14:15:15 +0200 Message-ID: <20261102121518.1197453-5-jarkko@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261102121518.1197453-1-jarkko@kernel.org> References: <20261102121518.1197453-1-jarkko@kernel.org> X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit key_garbage_collector() has a design that is not resistant enough for workqueue lockups. The duration scales up relative to the number of items in the serial tree, which causes a reoccuring theme of being guilty of causing workqueue lockups. Resolve the problem by processing in chunks: 1. Declare a static variable key_gc_work, which owns the garbage collection in-flight state, and key_schedule_gc_work() for re-scheduling the work. 2. Define KEY_GC_CHUNK_SIZE, set to 64 keys, as the bound for the number of items scanned and destroyed. 3. Define KEY_GC_DESTROYING to mark resume to destruction without repeating the RCU grace period. 4. Define KEY_GC_REAP_REQUESTED for preserving full-pass requests across the continuations. keygcbench results without the patch: unused: min=413.359 avg=1817.240 max=3221.120 var=1970880.024 expired: min=0.002 avg=1360.124 max=2481.990 var=1055093.994 combined: min=0.002 avg=1542.970 max=3221.120 var=1471557.422 keygcbench results with the patch: unused: min=0.005 avg=0.126 max=54.173 var=0.946 expired: min=0.002 avg=0.210 max=216.470 var=7.894 combined: min=0.002 avg=0.158 max=216.470 var=3.627 These results translate to: - >99.9% drop in the combined variance. - 3.0% increase in the total task time. The value 64 for KEY_GC_CHUNK_SIZE was cherry-picked from the set {1, 2, ..., 1024} by running the benchmark for each chunk size three times. At the far left variance is 97% lower but at the same time total time grows by 133%, when compared to the selected chunk size. The size was picked based on getting a reasonable variance with a minimal throughput decline. Fixes: 0c061b5707ab ("KEYS: Correctly destroy key payloads when their keytype is removed") Link: https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd-test.git/tree/package/keygcbench Signed-off-by: Jarkko Sakkinen --- security/keys/gc.c | 132 ++++++++++++++++++++++++++------------- security/keys/internal.h | 3 +- security/keys/key.c | 4 +- security/keys/keyring.c | 2 +- 4 files changed, 94 insertions(+), 47 deletions(-) diff --git a/security/keys/gc.c b/security/keys/gc.c index 876c30c019ad..fc1e5e39b828 100644 --- a/security/keys/gc.c +++ b/security/keys/gc.c @@ -11,16 +11,27 @@ #include #include "internal.h" -/* - * Delay between key revocation/expiry in seconds - */ -unsigned key_gc_delay = 5 * 60; +#define KEY_GC_CHUNK_SIZE 64 /* * Reaper for unused keys. */ static void key_garbage_collector(struct work_struct *work); -DECLARE_WORK(key_gc_work, key_garbage_collector); + +static struct { + time64_t start; /* expiry range start */ + time64_t end; /* expiry range end */ + struct rb_node *cursor; /* serial tree position */ + u8 state; /* state flags */ + struct work_struct work; /* work item */ +} key_gc_work = { + .work = __WORK_INITIALIZER(key_gc_work.work, key_garbage_collector), +}; + +/* + * Delay between key revocation/expiry in seconds + */ +unsigned int key_gc_delay = 5 * 60; /* * Reaper for links from keyrings to dead keys. @@ -31,6 +42,23 @@ static DEFINE_TIMER(key_gc_timer, key_gc_timer_func); static time64_t key_gc_next_run = TIME64_MAX; static unsigned long key_gc_flags; #define KEY_GC_KEY_EXPIRED 0 /* A key expired and needs unlinking */ +#define KEY_GC_REAP_REQUESTED 1 /* Another complete pass was requested */ + +/* + * Schedule a new GC pass or re-schedule an ongoing GC pass. + */ +void key_schedule_gc_work(bool expired) +{ + unsigned long flags = BIT(KEY_GC_REAP_REQUESTED); + + if (expired) + flags |= BIT(KEY_GC_KEY_EXPIRED); + + /* Publish all request flags together, after the caller's updates. */ + set_mask_bits(&key_gc_flags, 0, flags); + schedule_work(&key_gc_work.work); +} + /* * Schedule a garbage collection run. * - time precision isn't particularly important @@ -44,7 +72,8 @@ void key_schedule_gc(time64_t gc_at) if (gc_at <= now) { kdebug("IMMEDIATE"); - schedule_work(&key_gc_work); + /* Catch expirations that became due during the scan. */ + key_schedule_gc_work(true); } else if (gc_at < key_gc_next_run) { kdebug("DEFERRED"); key_gc_next_run = gc_at; @@ -66,15 +95,6 @@ void key_set_expiry(struct key *key, time64_t expiry) } } -/* - * Schedule a dead links collection run. - */ -void key_schedule_gc_links(void) -{ - set_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags); - schedule_work(&key_gc_work); -} - /* * Some key's cleanup time was met after it expired, so we need to get the * reaper to go through a cycle finding expired keys. @@ -83,7 +103,7 @@ static void key_gc_timer_func(struct timer_list *unused) { kenter(""); key_gc_next_run = TIME64_MAX; - key_schedule_gc_links(); + key_schedule_gc_work(true); } /* @@ -91,7 +111,9 @@ static void key_gc_timer_func(struct timer_list *unused) */ static noinline void key_gc_unused_keys(struct list_head *keys) { - while (!list_empty(keys)) { + unsigned int chunk = KEY_GC_CHUNK_SIZE; + + while (!list_empty(keys) && chunk--) { struct key *key = list_entry(keys->next, struct key, graveyard_link); struct module *owner = key->type->owner; @@ -137,35 +159,45 @@ static noinline void key_gc_unused_keys(struct list_head *keys) static void key_garbage_collector(struct work_struct *work) { static LIST_HEAD(graveyard); - u8 gc_state = 0; + typeof(key_gc_work) *gc = &key_gc_work; #define KEY_GC_REAP_AGAIN 0x01 /* - Need another cycle */ #define KEY_GC_REAPING_LINKS 0x02 /* - We need to reap links */ +#define KEY_GC_DESTROYING 0x04 /* - We need to destroy keys */ - struct rb_node *cursor; + unsigned int chunk = KEY_GC_CHUNK_SIZE; struct key *key; - time64_t new_timer, limit, expiry; + time64_t expiry; - kenter("[%lx]", key_gc_flags); + kenter("[%lx,%x]", key_gc_flags, gc->state); - limit = ktime_get_real_seconds(); + if (gc->state & KEY_GC_DESTROYING) + goto destroy_keys; + if (gc->cursor) { + spin_lock(&key_serial_lock); + goto continue_scanning; + } + test_and_clear_bit(KEY_GC_REAP_REQUESTED, &key_gc_flags); + gc->start = ktime_get_real_seconds(); + gc->state = 0; if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags)) - gc_state |= KEY_GC_REAPING_LINKS; - kdebug("new pass %x", gc_state); + gc->state |= KEY_GC_REAPING_LINKS; + kdebug("new pass %x", gc->state); - new_timer = TIME64_MAX; + gc->end = TIME64_MAX; /* As only this function is permitted to remove things from the key * serial tree, if cursor is non-NULL then it will always point to a * valid node in the tree - even if lock got dropped. */ spin_lock(&key_serial_lock); - cursor = rb_first(&key_serial_tree); + gc->cursor = rb_first(&key_serial_tree); continue_scanning: - while (cursor) { - key = rb_entry(cursor, struct key, serial_node); - cursor = rb_next(cursor); + while (gc->cursor && chunk) { + key = rb_entry(gc->cursor, struct key, serial_node); + gc->cursor = rb_next(gc->cursor); + chunk--; if (!test_bit_acquire(KEY_FLAG_USER_ALIVE, &key->flags)) { /* Clobber key->user after final put seen. */ @@ -176,14 +208,14 @@ static void key_garbage_collector(struct work_struct *work) if (expiry != TIME64_MAX) { if (!(key->type->flags & KEY_TYPE_INSTANT_REAP)) expiry += key_gc_delay; - if (expiry > limit && expiry < new_timer) { + if (expiry > gc->start && expiry < gc->end) { kdebug("will expire %x in %lld", - key_serial(key), key->expiry - limit); - new_timer = key->expiry; + key_serial(key), key->expiry - gc->start); + gc->end = key->expiry; } } - if ((gc_state & KEY_GC_REAPING_LINKS) && + if ((gc->state & KEY_GC_REAPING_LINKS) && key->type == &key_type_keyring) goto found_keyring; @@ -195,7 +227,11 @@ static void key_garbage_collector(struct work_struct *work) spin_unlock(&key_serial_lock); maybe_resched: - if (cursor) { + if (gc->cursor) { + if (!chunk) { + schedule_work(&key_gc_work.work); + return; + } cond_resched(); spin_lock(&key_serial_lock); goto continue_scanning; @@ -207,9 +243,9 @@ static void key_garbage_collector(struct work_struct *work) */ kdebug("pass complete"); - if (new_timer != TIME64_MAX) { - new_timer += key_gc_delay; - key_schedule_gc(new_timer); + if (gc->end != TIME64_MAX) { + gc->end += key_gc_delay; + key_schedule_gc(gc->end); } if (!list_empty(&graveyard)) { @@ -220,13 +256,25 @@ static void key_garbage_collector(struct work_struct *work) */ kdebug("gc sync"); synchronize_rcu(); + } + + gc->state |= KEY_GC_DESTROYING; + +destroy_keys: + if (!list_empty(&graveyard)) { kdebug("gc keys"); key_gc_unused_keys(&graveyard); + if (!list_empty(&graveyard)) { + schedule_work(&key_gc_work.work); + return; + } } + gc->state &= ~KEY_GC_DESTROYING; - if (gc_state & KEY_GC_REAP_AGAIN) - schedule_work(&key_gc_work); - kleave(" [end %x]", gc_state); + if ((gc->state & KEY_GC_REAP_AGAIN) || + test_bit(KEY_GC_REAP_REQUESTED, &key_gc_flags)) + schedule_work(&key_gc_work.work); + kleave(" [end %x]", gc->state); return; /* We found an unreferenced key - once we've removed it from the tree, @@ -238,7 +286,7 @@ static void key_garbage_collector(struct work_struct *work) spin_unlock(&key_serial_lock); list_add_tail(&key->graveyard_link, &graveyard); - gc_state |= KEY_GC_REAP_AGAIN; + gc->state |= KEY_GC_REAP_AGAIN; goto maybe_resched; /* We found a keyring and we need to check the payload for links to @@ -248,6 +296,6 @@ static void key_garbage_collector(struct work_struct *work) */ found_keyring: spin_unlock(&key_serial_lock); - keyring_gc(key, limit); + keyring_gc(key, gc->start); goto maybe_resched; } diff --git a/security/keys/internal.h b/security/keys/internal.h index 005d609ae2df..976f16baf632 100644 --- a/security/keys/internal.h +++ b/security/keys/internal.h @@ -161,12 +161,11 @@ extern bool lookup_user_key_possessed(const struct key *key, extern long join_session_keyring(const char *name); extern void key_change_session_keyring(struct callback_head *twork); -extern struct work_struct key_gc_work; extern unsigned key_gc_delay; extern void keyring_gc(struct key *keyring, time64_t limit); void key_set_expiry(struct key *key, time64_t expiry); extern void key_schedule_gc(time64_t gc_at); -extern void key_schedule_gc_links(void); +void key_schedule_gc_work(bool expired); extern int key_task_permission(const key_ref_t key_ref, const struct cred *cred, diff --git a/security/keys/key.c b/security/keys/key.c index f396e56d640f..e6569f89cca9 100644 --- a/security/keys/key.c +++ b/security/keys/key.c @@ -679,7 +679,7 @@ void key_put(struct key *key) } /* Mark key as safe for GC after key->user done. */ clear_bit_unlock(KEY_FLAG_USER_ALIVE, &key->flags); - schedule_work(&key_gc_work); + key_schedule_gc_work(false); } } } @@ -1200,7 +1200,7 @@ void key_invalidate(struct key *key) down_write_nested(&key->sem, 1); if (!test_and_set_bit(KEY_FLAG_INVALIDATED, &key->flags)) { notify_key(key, NOTIFY_KEY_INVALIDATED, 0); - key_schedule_gc_links(); + key_schedule_gc_work(true); } up_write(&key->sem); } diff --git a/security/keys/keyring.c b/security/keys/keyring.c index 94a886a84bd6..b2ae7a65b186 100644 --- a/security/keys/keyring.c +++ b/security/keys/keyring.c @@ -266,7 +266,7 @@ void key_remove_domain(struct key_tag *domain_tag) { domain_tag->removed = true; if (!key_put_tag(domain_tag)) - key_schedule_gc_links(); + key_schedule_gc_work(true); } /* -- 2.47.3