net: Make napi_hash_lock irq safe

JIRA: https://issues.redhat.com/browse/RHEL-77816
Upstream Status: net.git commit cecc155

commit cecc155
Author: Joe Damato <jdamato@fastly.com>
Date:   Mon Dec 2 18:21:02 2024 +0000

    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: 86e25f4 ("net: napi: Add napi_config")
    Reported-by: Guenter Roeck <linux@roeck-us.net>
    Closes: https://lore.kernel.org/netdev/85dd4590-ea6b-427d-876a-1d8559c7ad82@roeck-us.net/
    Suggested-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Joe Damato <jdamato@fastly.com>
    Tested-by: Guenter Roeck <linux@roeck-us.net>
    Reviewed-by: Eric Dumazet <edumazet@google.com>
    Link: https://patch.msgid.link/20241202182103.363038-1-jdamato@fastly.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Davide Caratti <dcaratti@redhat.com>

Author: dcaratti

net/core/dev.c

@@ -6457,18 +6457,22 @@ 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 {
@@ -6478,19 +6482,21 @@ 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
  * is respected before freeing memory containing @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)