[PATCH net v2] net: ag71xx: re-enable TX interrupts on RX OOM

[PATCH net v2] net: ag71xx: re-enable TX interrupts on RX OOM

[Rosen Penev]

When the RX ring runs out of buffers the OOM path calls
napi_complete() but does not re-enable interrupts.  Because
INT_POLL masks both RX and TX events, TX completions are
blocked until the OOM timer fires (~100 ms), which can cause
TX ring exhaustion and dropped packets.

Restore TX interrupt delivery so the engine can drain completed
descriptors while NAPI waits for RX buffer memory.

Fixes: d51b6ce441d3 ("net: ethernet: add ag71xx driver")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 v2: add Fixes: . 
 drivers/net/ethernet/atheros/ag71xx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/atheros/ag71xx.c b/drivers/net/ethernet/atheros/ag71xx.c
index d93fd91ff884..5a33759be3cf 100644
--- a/drivers/net/ethernet/atheros/ag71xx.c
+++ b/drivers/net/ethernet/atheros/ag71xx.c
@@ -1746,6 +1746,7 @@ static int ag71xx_poll(struct napi_struct *napi, int limit)
 
 	mod_timer(&ag->oom_timer, jiffies + AG71XX_OOM_REFILL);
 	napi_complete(napi);
+	ag71xx_int_enable(ag, AG71XX_INT_TX);
 	return 0;
 }
 
-- 
2.56.0

Re: [PATCH net v2] net: ag71xx: re-enable TX interrupts on RX OOM

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - How the issue was discovered, e.g. hit in production, hit during
   development, syzbot report, manual code inspection, LLM or static
   analysis tool scan.

 - Whether the issue was actually triggered, or is only theoretical
   (e.g. found by code inspection). If it was triggered please include
   the symptoms, like the stack trace or error messages.

 - What hardware the change was tested on. For driver fixes please
   mention the device (and if relevant firmware version) used for
   testing, or say that the change was not tested on real hardware.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.

Re: [PATCH net v2] net: ag71xx: re-enable TX interrupts on RX OOM

[Daniel Machon]

> When the RX ring runs out of buffers the OOM path calls
> napi_complete() but does not re-enable interrupts.  Because
> INT_POLL masks both RX and TX events, TX completions are
> blocked until the OOM timer fires (~100 ms), which can cause
> TX ring exhaustion and dropped packets.

Is that not exactly what the OOM timer is for? It schedules napi and tx buffers
will eventually be freed. I mean, it seems like it was designed to work like
this.

> 
> Restore TX interrupt delivery so the engine can drain completed
> descriptors while NAPI waits for RX buffer memory.
> 
> Fixes: d51b6ce441d3 ("net: ethernet: add ag71xx driver")
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>  v2: add Fixes: . 
>  drivers/net/ethernet/atheros/ag71xx.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/ethernet/atheros/ag71xx.c b/drivers/net/ethernet/atheros/ag71xx.c
> index d93fd91ff884..5a33759be3cf 100644
> --- a/drivers/net/ethernet/atheros/ag71xx.c
> +++ b/drivers/net/ethernet/atheros/ag71xx.c
> @@ -1746,6 +1746,7 @@ static int ag71xx_poll(struct napi_struct *napi, int limit)
>  
>  	mod_timer(&ag->oom_timer, jiffies + AG71XX_OOM_REFILL);
>  	napi_complete(napi);
> +	ag71xx_int_enable(ag, AG71XX_INT_TX);
>  	return 0;
>  }
>  
> -- 
> 2.56.0
> 

/Daniel