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net: prevent deadlocks when enabling NAPIs with mixed kthread config

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The following order of calls currently deadlocks if:
 - device has threaded=1; and
 - NAPI has persistent config with threaded=0.

  netif_napi_add_weight_config()
    dev->threaded == 1
      napi_kthread_create()

  napi_enable()
    napi_restore_config()
      napi_set_threaded(0)
        napi_stop_kthread()
	  while (NAPIF_STATE_SCHED)
	    msleep(20)

We deadlock because disabled NAPI has STATE_SCHED set.
Creating a thread in netif_napi_add() just to destroy it in
napi_disable() is fairly ugly in the first place. Let's read
both the device config and the NAPI config in netif_napi_add().

Fixes: e6d7626881 ("net: Update threaded state in napi config in netif_set_threaded")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Joe Damato <joe@dama.to>
Link: https://patch.msgid.link/20250809001205.1147153-4-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Jakub Kicinski 2025-08-08 17:12:05 -07:00 • committed by Paolo Abeni
parent ccba9f6baa
commit b3fc08ab9a
2 changed files with 11 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

3
net/core/dev.c
View file

@ -7357,7 +7357,8 @@ void netif_napi_add_weight_locked(struct net_device *dev,
* Clear dev->threaded if kthread creation failed so that
* threaded mode will not be enabled in napi_enable().
*/
if (dev->threaded && napi_kthread_create(napi))
if (napi_get_threaded_config(dev, napi))
if (napi_kthread_create(napi))
dev->threaded = NETDEV_NAPI_THREADED_DISABLED;
netif_napi_set_irq_locked(napi, -1);
}

8
net/core/dev.h
View file

@ -323,6 +323,14 @@ static inline enum netdev_napi_threaded napi_get_threaded(struct napi_struct *n)
return NETDEV_NAPI_THREADED_DISABLED;
}
static inline enum netdev_napi_threaded
napi_get_threaded_config(struct net_device *dev, struct napi_struct *n)
{
if (n->config)
return n->config->threaded;
return dev->threaded;
}
int napi_set_threaded(struct napi_struct *n,
enum netdev_napi_threaded threaded);