Re: [PATCH v2 1/2] net/mlx5: check for no data read in devx interrupt

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri,  6 Feb 2026 17:20:53 +0000
Kevin Traynor <ktraynor@redhat.com> wrote:

> A busy-loop may occur when there are EPOLLERR, EPOLLHUP or
> EPOLLRDHUP epoll events for the devx interrupt fd.
> 
> This may happen if the interrupt fd is deleted, if the device
> is unbound from mlx5_core kernel driver or if the device is
> removed by the mlx5 kernel driver as part of LAG setup.
> 
> When that occurs, there is no data to be read and in the devx
> interrupt handler an EAGAIN is returned on the first call to
> devx_get_async_cmd_comp, but this is not checked.
> 
> As the interrupt is not removed or condition reset, it causes
> an interrupt processing busy-loop, which leads to the dpdk-intr
> thread going to 100% CPU.
> 
> e.g.
> epoll_wait
>    (6, [{events=EPOLLIN|EPOLLRDHUP, data={u32=28, u64=28}}], 8, -1) = 1
> read(28, 0x7f1f5c7fc2f0, 40)
>    = -1 EAGAIN (Resource temporarily unavailable)
> epoll_wait
>    (6, [{events=EPOLLIN|EPOLLRDHUP, data={u32=28, u64=28}}], 8, -1) = 1
> read(28, 0x7f1f5c7fc2f0, 40)
>    = -1 EAGAIN (Resource temporarily unavailable)
> 
> Add a check for an EAGAIN return from devx_get_async_cmd_comp on the
> first read. If that happens, unregister the callback to prevent looping.
> 
> Bugzilla ID: 1873
> Fixes: f15db67df09c ("net/mlx5: accelerate DV flow counter query")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Kevin Traynor <ktraynor@redhat.com>

AI spotted this, I didn't...


Errors:

    Line 139: Unnecessary semicolon after closing brace

c

   };

Should be:
c

   }

    Lines 142-146: Block comment uses incorrect style Block comments in C code should use /* and */ style, not /** which is reserved for documentation comments.

c

   /**
    * no data and EAGAIN indicate there is an error or
    * disconnect state. Unregister callback to prevent
    * interrupt busy-looping.
    */

Should be:
c

   /*
    * no data and EAGAIN indicate there is an error or
    * disconnect state. Unregister callback to prevent
    * interrupt busy-looping.
    */

Warnings:

    Logic clarity: The variable data_read is set to true inside the while loop but never checked when data WAS read. Consider if data_read is the clearest way to express this condition.