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Commit 13baa00a authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: net_enable_timestamp() can be called from irq contexts 



It is now very clear that silly TCP listeners might play with
enabling/disabling timestamping while new children are added
to their accept queue.

Meaning net_enable_timestamp() can be called from BH context
while current state of the static key is not enabled.

Lets play safe and allow all contexts.

The work queue is scheduled only under the problematic cases,
which are the static key enable/disable transition, to not slow down
critical paths.

This extends and improves what we did in commit 5fa8bbda ("net: use
a work queue to defer net_disable_timestamp() work")

Fixes: b90e5794 ("net: dont call jump_label_dec from irq context")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 540e2894

net/core/dev.c

+31 −4
Original line number Diff line number Diff line
@@ -1698,27 +1698,54 @@ EXPORT_SYMBOL_GPL(net_dec_egress_queue); 
static struct static_key netstamp_needed __read_mostly;

#ifdef HAVE_JUMP_LABEL

static atomic_t netstamp_needed_deferred;

static atomic_t netstamp_wanted;

static void netstamp_clear(struct work_struct *work)

{

	int deferred = atomic_xchg(&netstamp_needed_deferred, 0);

	int wanted;



	while (deferred--)

		static_key_slow_dec(&netstamp_needed);

	wanted = atomic_add_return(deferred, &netstamp_wanted);

	if (wanted > 0)

		static_key_enable(&netstamp_needed);

	else

		static_key_disable(&netstamp_needed);

}

static DECLARE_WORK(netstamp_work, netstamp_clear);

#endif



void net_enable_timestamp(void)

{

#ifdef HAVE_JUMP_LABEL

	int wanted;



	while (1) {

		wanted = atomic_read(&netstamp_wanted);

		if (wanted <= 0)

			break;

		if (atomic_cmpxchg(&netstamp_wanted, wanted, wanted + 1) == wanted)

			return;

	}

	atomic_inc(&netstamp_needed_deferred);

	schedule_work(&netstamp_work);

#else

	static_key_slow_inc(&netstamp_needed);

#endif

}

EXPORT_SYMBOL(net_enable_timestamp);



void net_disable_timestamp(void)

{

#ifdef HAVE_JUMP_LABEL

	/* net_disable_timestamp() can be called from non process context */

	atomic_inc(&netstamp_needed_deferred);

	int wanted;



	while (1) {

		wanted = atomic_read(&netstamp_wanted);

		if (wanted <= 1)

			break;

		if (atomic_cmpxchg(&netstamp_wanted, wanted, wanted - 1) == wanted)

			return;

	}

	atomic_dec(&netstamp_needed_deferred);

	schedule_work(&netstamp_work);

#else

	static_key_slow_dec(&netstamp_needed);