On Mon, Dec 02, 2024 at 06:21:02PM +0000, Joe Damato wrote:

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: 86e25f40aa1e ("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... Suggested-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Joe Damato jdamato@fastly.com

Tested-by: Guenter Roeck linux@roeck-us.net

---

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