netdev - [net] net: Make napi_hash

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Message-Id: <20241202182103.363038-1-jdamato@fastly.com>
Date: Mon,  2 Dec 2024 18:21:02 +0000
From: Joe Damato <jdamato@...tly.com>
To: netdev@...r.kernel.org
Cc: pabeni@...hat.com,
	edumazet@...gle.com,
	kuba@...nel.org,
	mkarsten@...terloo.ca,
	Joe Damato <jdamato@...tly.com>,
	stable@...r.kernel.org,
	Guenter Roeck <linux@...ck-us.net>,
	"David S. Miller" <davem@...emloft.net>,
	Simon Horman <horms@...nel.org>,
	David Ahern <dsahern@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	linux-kernel@...r.kernel.org (open list)
Subject: [net] 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@...r.kernel.org
Fixes: 86e25f40aa1e ("net: napi: Add napi_config")
Reported-by: Guenter Roeck <linux@...ck-us.net>
Closes: https://lore.kernel.org/netdev/85dd4590-ea6b-427d-876a-1d8559c7ad82@roeck-us.net/
Suggested-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Joe Damato <jdamato@...tly.com>
---
 net/core/dev.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 13d00fc10f55..45a8c3dd4a64 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -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)
-- 
2.25.1