Commit cecc1555 authored by Joe Damato's avatar Joe Damato Committed by Jakub Kicinski
Browse files

net: Make napi_hash_lock irq safe 



Make napi_hash_lock IRQ safe. It is used during the control path, and is
taken and released in napi_hash_add and napi_hash_del, which will
typically be called by calls to napi_enable and napi_disable.

This change avoids a deadlock in pcnet32 (and other any other drivers
which follow the same pattern):

 CPU 0:
 pcnet32_open
    spin_lock_irqsave(&lp->lock, ...)
      napi_enable
        napi_hash_add <- before this executes, CPU 1 proceeds
          spin_lock(napi_hash_lock)
       [...]
    spin_unlock_irqrestore(&lp->lock, flags);

 CPU 1:
   pcnet32_close
     napi_disable
       napi_hash_del
         spin_lock(napi_hash_lock)
          < INTERRUPT >
            pcnet32_interrupt
              spin_lock(lp->lock) <- DEADLOCK

Changing the napi_hash_lock to be IRQ safe prevents the IRQ from firing
on CPU 1 until napi_hash_lock is released, preventing the deadlock.

Cc: stable@vger.kernel.org
Fixes: 86e25f40 ("net: napi: Add napi_config")
Reported-by: default avatarGuenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/netdev/85dd4590-ea6b-427d-876a-1d8559c7ad82@roeck-us.net/


Suggested-by: default avatarJakub Kicinski <kuba@kernel.org>
Signed-off-by: default avatarJoe Damato <jdamato@fastly.com>
Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20241202182103.363038-1-jdamato@fastly.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent af8edaed

net/core/dev.c

+12 −6
Original line number Diff line number Diff line
@@ -6557,18 +6557,22 @@ static void __napi_hash_add_with_id(struct napi_struct *napi, 
static void napi_hash_add_with_id(struct napi_struct *napi,

				  unsigned int napi_id)

{

	spin_lock(&napi_hash_lock);

	unsigned long flags;



	spin_lock_irqsave(&napi_hash_lock, flags);

	WARN_ON_ONCE(napi_by_id(napi_id));

	__napi_hash_add_with_id(napi, napi_id);

	spin_unlock(&napi_hash_lock);

	spin_unlock_irqrestore(&napi_hash_lock, flags);

}



static void napi_hash_add(struct napi_struct *napi)

{

	unsigned long flags;



	if (test_bit(NAPI_STATE_NO_BUSY_POLL, &napi->state))

		return;



	spin_lock(&napi_hash_lock);

	spin_lock_irqsave(&napi_hash_lock, flags);



	/* 0..NR_CPUS range is reserved for sender_cpu use */

	do {
@@ -6578,7 +6582,7 @@ static void napi_hash_add(struct napi_struct *napi) 


	__napi_hash_add_with_id(napi, napi_gen_id);



	spin_unlock(&napi_hash_lock);

	spin_unlock_irqrestore(&napi_hash_lock, flags);

}



/* Warning : caller is responsible to make sure rcu grace period
@@ -6586,11 +6590,13 @@ static void napi_hash_add(struct napi_struct *napi) 
 */

static void napi_hash_del(struct napi_struct *napi)

{

	spin_lock(&napi_hash_lock);

	unsigned long flags;



	spin_lock_irqsave(&napi_hash_lock, flags);



	hlist_del_init_rcu(&napi->napi_hash_node);



	spin_unlock(&napi_hash_lock);

	spin_unlock_irqrestore(&napi_hash_lock, flags);

}



static enum hrtimer_restart napi_watchdog(struct hrtimer *timer)