Commit 585aa621 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Jakub Kicinski
Browse files

net/tcp_sigpool: Use nested-BH locking for sigpool_scratch. 



sigpool_scratch is a per-CPU variable and relies on disabled BH for its
locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT
this data structure requires explicit locking.

Make a struct with a pad member (original sigpool_scratch) and a
local_lock_t and use local_lock_nested_bh() for locking. This change
adds only lockdep coverage and does not alter the functional behaviour
for !PREEMPT_RT.

Cc: David Ahern <dsahern@kernel.org>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20240620132727.660738-6-bigeasy@linutronix.de


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent bdacf3e3

net/ipv4/tcp_sigpool.c

+13 −4
Original line number Diff line number Diff line
@@ -10,7 +10,14 @@ 
#include <net/tcp.h>



static size_t __scratch_size;

static DEFINE_PER_CPU(void __rcu *, sigpool_scratch);

struct sigpool_scratch {

	local_lock_t bh_lock;

	void __rcu *pad;

};



static DEFINE_PER_CPU(struct sigpool_scratch, sigpool_scratch) = {

	.bh_lock = INIT_LOCAL_LOCK(bh_lock),

};



struct sigpool_entry {

	struct crypto_ahash	*hash;
@@ -72,7 +79,7 @@ static int sigpool_reserve_scratch(size_t size) 
			break;

		}



		old_scratch = rcu_replace_pointer(per_cpu(sigpool_scratch, cpu),

		old_scratch = rcu_replace_pointer(per_cpu(sigpool_scratch.pad, cpu),

					scratch, lockdep_is_held(&cpool_mutex));

		if (!cpu_online(cpu) || !old_scratch) {

			kfree(old_scratch);
@@ -93,7 +100,7 @@ static void sigpool_scratch_free(void) 
	int cpu;



	for_each_possible_cpu(cpu)

		kfree(rcu_replace_pointer(per_cpu(sigpool_scratch, cpu),

		kfree(rcu_replace_pointer(per_cpu(sigpool_scratch.pad, cpu),

					  NULL, lockdep_is_held(&cpool_mutex)));

	__scratch_size = 0;

}
@@ -277,7 +284,8 @@ int tcp_sigpool_start(unsigned int id, struct tcp_sigpool *c) __cond_acquires(RC 
	/* Pairs with tcp_sigpool_reserve_scratch(), scratch area is

	 * valid (allocated) until tcp_sigpool_end().

	 */

	c->scratch = rcu_dereference_bh(*this_cpu_ptr(&sigpool_scratch));

	local_lock_nested_bh(&sigpool_scratch.bh_lock);

	c->scratch = rcu_dereference_bh(*this_cpu_ptr(&sigpool_scratch.pad));

	return 0;

}

EXPORT_SYMBOL_GPL(tcp_sigpool_start);
@@ -286,6 +294,7 @@ void tcp_sigpool_end(struct tcp_sigpool *c) __releases(RCU_BH) 
{

	struct crypto_ahash *hash = crypto_ahash_reqtfm(c->req);



	local_unlock_nested_bh(&sigpool_scratch.bh_lock);

	rcu_read_unlock_bh();

	ahash_request_free(c->req);

	crypto_free_ahash(hash);