From: Joe Damato <joe@dama.to>
To: Jakub Kicinski <kuba@kernel.org>
Cc: davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com,
pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org,
willemdebruijn.kernel@gmail.com, skhawaja@google.com,
sdf@fomichev.me, shuah@kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH net v2 3/3] net: prevent deadlocks when enabling NAPIs with mixed kthread config
Date: Sat, 9 Aug 2025 19:05:52 -0700 [thread overview]
Message-ID: <aJf-gL4n6xF5V-rk@MacBook-Air.local> (raw)
In-Reply-To: <20250809001205.1147153-4-kuba@kernel.org>
On Fri, Aug 08, 2025 at 05:12:05PM -0700, Jakub Kicinski wrote:
> 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: e6d76268813d ("net: Update threaded state in napi config in netif_set_threaded")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> net/core/dev.h | 8 ++++++++
> net/core/dev.c | 5 +++--
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
Reviewed-by: Joe Damato <joe@dama.to>
next prev parent reply other threads:[~2025-08-10 2:05 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-09 0:12 [PATCH net v2 0/3] net: prevent deadlocks and mis-configuration with per-NAPI threaded config Jakub Kicinski
2025-08-09 0:12 ` [PATCH net v2 1/3] selftests: drv-net: don't assume device has only 2 queues Jakub Kicinski
2025-08-10 2:01 ` Joe Damato
2025-08-09 0:12 ` [PATCH net v2 2/3] net: update NAPI threaded config even for disabled NAPIs Jakub Kicinski
2025-08-10 2:04 ` Joe Damato
2025-08-09 0:12 ` [PATCH net v2 3/3] net: prevent deadlocks when enabling NAPIs with mixed kthread config Jakub Kicinski
2025-08-10 2:05 ` Joe Damato [this message]
2025-08-10 1:59 ` [PATCH net v2 0/3] net: prevent deadlocks and mis-configuration with per-NAPI threaded config Joe Damato
2025-08-11 15:52 ` Jakub Kicinski
2025-08-12 12:50 ` patchwork-bot+netdevbpf
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