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Subject[PATCH 1/7] static_key: flush rate limit timer on rmmod
Date
Fix a bug when we free module memory while timer is pending by marking
deferred static keys and flushing the timer on module unload.

Also make static_key_rate_limit() useable more than once.

Reproducer: (host crasher)
modprobe kvm_intel
(sleep 1; echo quit) \
| qemu-kvm -kernel /dev/null -monitor stdio &
sleep 0.5
until modprobe -rv kvm_intel 2>/dev/null; do true; done
modprobe -v kvm_intel

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
Very hacky; I've already queued generalizing ratelimit and applying it
here, but there is still a lot to do on static keys ...

include/linux/jump_label.h | 1 +
kernel/jump_label.c | 17 ++++++++++++++++-
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index a507907..848bd15 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -58,6 +58,7 @@ struct static_key {
#ifdef CONFIG_MODULES
struct static_key_mod *next;
#endif
+ atomic_t deferred;
};

# include <asm/jump_label.h>
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 297a924..7018042 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -116,8 +116,9 @@ EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
void jump_label_rate_limit(struct static_key_deferred *key,
unsigned long rl)
{
+ if (!atomic_xchg(&key->key.deferred, 1))
+ INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
key->timeout = rl;
- INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
}
EXPORT_SYMBOL_GPL(jump_label_rate_limit);

@@ -185,6 +186,14 @@ static enum jump_label_type jump_label_type(struct static_key *key)
return JUMP_LABEL_DISABLE;
}

+static void static_key_rate_limit_flush(struct static_key *key)
+{
+ struct static_key_deferred *dkey =
+ container_of(key, struct static_key_deferred, key);
+ if (atomic_read(&key->deferred))
+ flush_delayed_work(&dkey->work);
+}
+
void __init jump_label_init(void)
{
struct jump_entry *iter_start = __start___jump_table;
@@ -334,6 +343,12 @@ static void jump_label_del_module(struct module *mod)

key = (struct static_key *)(unsigned long)iter->key;

+ /* We could also check if the static_key is used in its
+ * defining module and skip this flush then.
+ * (Rewrite of ratelimit in planned, so we don't care much)
+ */
+ static_key_rate_limit_flush(key);
+
if (__module_address(iter->key) == mod)
continue;

--
1.8.3.1
--
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