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=1793393662; b=cKiKK6Mf2Z9OAv4v9IrPOjSXBWCcCZdQrWDxgXpCXrHUoHwWriiHYCHRLYMW53wKDAHP m2bHEu3wQ4iN28pTM6zUU4msTMpaqQTax9qfhjECGXYIQz7fXd59iU7jc1LG3ditvwln1 B4+2yGql14srj4VuEdhoffxSYGE42ak57nZyxgZp0324aaCPsWjAJVOXt4RDOA8KNhk+X 7i9LyvgHJST1XMXT52pifgxn+UZ54vObiaNBkBwX9wfk2nR/e6oSHw1/8LdrZtp1Nx5Ob dTLwTxaV3S8Ilnn/B7wbib9AEmWFqsWt7eB+qFNBgw+ysZlDHDgq1Y7XeaSCJEhpJtg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793393662; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Transfer-Encoding; bh=qCervv7eb/iHyiJerXTtmo8FfBpq+tzA8F5cSzqXS7A=; b=0hgxt5880h8orC8KVevIbsw/tXsyqV3Mj+66yCnvqSq0PpWQU6eRmUxiyyi/FijS8TBH rZ0pOmoMUJ+Upbbn1h8Up4nM/T+WJ0FnhxM7cOB4Xrw+urIHgD0ZC/hfMQSQK5M2d8OaT O3Ula3p9m3BStgjHKMZQ10oohJTkx025EY+2AHz6YPdQynMeifjSEALjkgCDIfXyOFQu0 QAqdB3DTibLlxRWv3nzqeoTVKsiVZEaCxcj1NnjjP3++19zO/fcMyT1sIG7f+zNhUqP7n iUNG/MUzAHdqHd8oSxDpjw/uQSks0wXHy3cc24WRAWhgjcsWPnJV6mYHXenHYh3UDlQ== 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=TpyBDpZy; 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 66065606A31C; Fri, 30 Oct 2026 20:54:22 +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=TpyBDpZy Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id B34131F00A15; Fri, 30 Oct 2026 20:54:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793393662; bh=qCervv7eb/iHyiJerXTtmo8FfBpq+tzA8F5cSzqXS7A=; h=From:To:Cc:Subject:Date; b=TpyBDpZycoC4Tpblz+KL7GE+HybWv0yqUxx5dfdbB1pmba4zzE+orAaQP2u25Brp7 338icqOMZUTnnD1+MWL2HXcxmfvqNl86J8E9ALqQEXuqKI4nEZu29S+7dXPaRYhyvA 5kdLfySQUF1IzojiZn8jqGdxne+ouGoBZ/UYh9qL2K/ybD3SxvG5KYvvlfZ6n8VgaS 4rxDsITJt9L9vbcjkVklNjBGTK9yv+eMt0J3PcTqsKzIKv4RVaYE6UDhq88ABGknQt Zla5VU03h93cwBocg76Ju+2cnIWpI5gYYZFgaEJQBOxeIgBJi1PuzlpxxmyVP9feRF KPOUED3uFWJdg== From: Jarkko Sakkinen To: David Howells Cc: Eric Biggers , linux-integrity@vger.kernel.org, Mimi Zohar , Jarkko Sakkinen , syzbot+c15de43f1e7fffbb7b9b@syzkaller.appspotmail.com, 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: [PATCH v8] KEYS: key_garbage_collector(): process in chunks Date: Fri, 30 Oct 2026 22:54:08 +0200 Message-ID: <20261030205412.3138975-1-jarkko@kernel.org> X-Mailer: git-send-email 2.47.3 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. Drain the graveyard before advancing key-type reaping. 4. Define KEY_GC_REAP_REQUESTED for preserving full-pass requests across the continuations. keygcbench results without the patch: unused: min=798.785 avg=4181.989 max=7565.193 var=11446068.927 expired: min=0.003 avg=2404.971 max=4111.065 var=3061018.501 combined: min=0.003 avg=3115.778 max=7565.193 var=7172908.943 keygcbench results with the patch: unused: min=0.005 avg=0.125 max=79.590 var=1.088 expired: min=0.002 avg=0.196 max=236.207 var=8.121 combined: min=0.002 avg=0.154 max=236.207 var=3.912 These results translate to: - 93% drop in the combined variance. - 2.2% 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") Reported-by: syzbot+c15de43f1e7fffbb7b9b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=c15de43f1e7fffbb7b9b Link: https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd-test.git/tree/package/keygcbench Signed-off-by: Jarkko Sakkinen --- v8: - Call key_schedule_gc_work(false) from key_put() to avoid unnecessary expired-link scans when freeing unreferenced keys, as reported by Sashiko: https://sashiko.dev/#/patchset/20261030202457.3058665-1-jarkko%40kernel.org v7: - Removed forgotten Closes tag for syzkaller. - Sashiko was right in that key_gc_schedule_links() should be called to mark expiry [1]. I fixed up the call site and also added expired bool parameter to key_gc_schedule_work() so that bits can be set in a single atomic operation. https://sashiko.dev/#/patchset/20261030160924.2919363-1-jarkko%40kernel.org v6: - Removed syzkaller references, given feedback: https://lore.kernel.org/keyrings/20261029234149.218-1-hdanton@sina.com/ v5: - Benchmarked all the chunk sizes in {1, 2, ..., 1024} and cherry-picked based on that the chunk size of 64. v4: - Added syzkaller link, as the resolution can be reasoned from the benchmark results. v3: - Added new tests results made by using keygcbench. - Added link to keygcbench. v2: - Fixed typo in the commit message. - Drop the local variable gc_state. security/keys/gc.c | 162 +++++++++++++++++++++++++-------------- security/keys/internal.h | 3 +- security/keys/key.c | 4 +- security/keys/keyring.c | 2 +- 4 files changed, 107 insertions(+), 64 deletions(-) diff --git a/security/keys/gc.c b/security/keys/gc.c index eda445f815d4..ea2efde5f33f 100644 --- a/security/keys/gc.c +++ b/security/keys/gc.c @@ -10,16 +10,27 @@ #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. @@ -34,6 +45,7 @@ static unsigned long key_gc_flags; #define KEY_GC_KEY_EXPIRED 0 /* A key expired and needs unlinking */ #define KEY_GC_REAP_KEYTYPE 1 /* A keytype is being unregistered */ #define KEY_GC_REAPING_KEYTYPE 2 /* Cleared when keytype reaped */ +#define KEY_GC_REAP_REQUESTED 3 /* Another complete pass was requested */ /* @@ -44,6 +56,21 @@ struct key_type key_type_dead = { .name = ".dead", }; +/* + * 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 @@ -57,7 +84,8 @@ void key_schedule_gc(time64_t gc_at) if (gc_at <= now || test_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) { 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; @@ -79,15 +107,6 @@ 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. @@ -96,7 +115,7 @@ 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); } /* @@ -119,7 +138,7 @@ void key_gc_keytype(struct key_type *ktype) set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags); kdebug("schedule"); - schedule_work(&key_gc_work); + key_schedule_gc_work(false); kdebug("sleep"); wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE, @@ -134,7 +153,9 @@ void key_gc_keytype(struct key_type *ktype) */ 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); short state = key->state; @@ -178,54 +199,64 @@ static noinline void key_gc_unused_keys(struct list_head *keys) static void key_garbage_collector(struct work_struct *work) { static LIST_HEAD(graveyard); - static u8 gc_state; /* Internal persistent state */ + 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 */ #define KEY_GC_REAPING_DEAD_1 0x10 /* - We need to mark dead keys */ #define KEY_GC_REAPING_DEAD_2 0x20 /* - We need to reap dead key links */ #define KEY_GC_REAPING_DEAD_3 0x40 /* - We need to reap dead keys */ #define KEY_GC_FOUND_DEAD_KEY 0x80 /* - We found at least one dead key */ - 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,%x]", key_gc_flags, gc_state); + 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(); /* Work out what we're going to be doing in this pass */ - gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2; - gc_state <<= 1; + gc->state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2; + gc->state <<= 1; if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags)) - gc_state |= KEY_GC_REAPING_LINKS; + gc->state |= KEY_GC_REAPING_LINKS; if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) - gc_state |= KEY_GC_REAPING_DEAD_1; - kdebug("new pass %x", gc_state); + gc->state |= KEY_GC_REAPING_DEAD_1; + 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. */ goto found_unreferenced_key; } - if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) { + if (unlikely(gc->state & KEY_GC_REAPING_DEAD_1)) { if (key->type == key_gc_dead_keytype) { - gc_state |= KEY_GC_FOUND_DEAD_KEY; + gc->state |= KEY_GC_FOUND_DEAD_KEY; set_bit(KEY_FLAG_DEAD, &key->flags); key->perm = 0; goto skip_dead_key; @@ -239,24 +270,24 @@ 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 (unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) + if (unlikely(gc->state & KEY_GC_REAPING_DEAD_2)) if (key->type == key_gc_dead_keytype) - gc_state |= KEY_GC_FOUND_DEAD_KEY; + gc->state |= KEY_GC_FOUND_DEAD_KEY; - if ((gc_state & KEY_GC_REAPING_LINKS) || - unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) { + if ((gc->state & KEY_GC_REAPING_LINKS) || + unlikely(gc->state & KEY_GC_REAPING_DEAD_2)) { if (key->type == &key_type_keyring) goto found_keyring; } - if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) + if (unlikely(gc->state & KEY_GC_REAPING_DEAD_3)) if (key->type == key_gc_dead_keytype) goto destroy_dead_key; @@ -269,7 +300,11 @@ 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; @@ -281,12 +316,12 @@ 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 (unlikely(gc_state & KEY_GC_REAPING_DEAD_2) || + if (unlikely(gc->state & KEY_GC_REAPING_DEAD_2) || !list_empty(&graveyard)) { /* Make sure that all pending keyring payload destructions are * fulfilled and that people aren't now looking at dead or @@ -297,33 +332,42 @@ static void key_garbage_collector(struct work_struct *work) 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 (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 | + if (unlikely(gc->state & (KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2))) { - if (!(gc_state & KEY_GC_FOUND_DEAD_KEY)) { + if (!(gc->state & KEY_GC_FOUND_DEAD_KEY)) { /* No remaining dead keys: short circuit the remaining * keytype reap cycles. */ kdebug("dead short"); - gc_state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2); - gc_state |= KEY_GC_REAPING_DEAD_3; + gc->state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2); + gc->state |= KEY_GC_REAPING_DEAD_3; } else { - gc_state |= KEY_GC_REAP_AGAIN; + gc->state |= KEY_GC_REAP_AGAIN; } } - if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) { + if (unlikely(gc->state & KEY_GC_REAPING_DEAD_3)) { kdebug("dead wake"); clear_and_wake_up_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags); } - 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, @@ -335,7 +379,7 @@ 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 restricted keyring and need to update the restriction if @@ -353,7 +397,7 @@ 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; /* We found a dead key that is still referenced. Reset its type and diff --git a/security/keys/internal.h b/security/keys/internal.h index b7b622bc36a1..33aa9bce3bb9 100644 --- a/security/keys/internal.h +++ b/security/keys/internal.h @@ -162,14 +162,13 @@ 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); extern void keyring_restriction_gc(struct key *keyring, struct key_type *dead_type); 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 void key_gc_keytype(struct key_type *ktype); extern int key_task_permission(const key_ref_t key_ref, diff --git a/security/keys/key.c b/security/keys/key.c index e88548f1a704..dd7a72c09cc9 100644 --- a/security/keys/key.c +++ b/security/keys/key.c @@ -670,7 +670,7 @@ 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); } } } @@ -1189,7 +1189,7 @@ 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 5281da9d5bf7..40e3b2b6aca1 100644 --- a/security/keys/keyring.c +++ b/security/keys/keyring.c @@ -265,7 +265,7 @@ 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