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When the driver activates the channels, it assumes NAPI isn't running
yet. mlx5e_activate_rq posts a NOP WQE to ICOSQ to trigger a hardware
interrupt and start NAPI, which will run mlx5e_alloc_rx_mpwqe and post
UMR WQEs to ICOSQ to be able to receive packets with striding RQ.
Unfortunately, a race condition is possible if NAPI is triggered by
something else (for example, TX) at a bad timing, before
mlx5e_activate_rq finishes. In this case, mlx5e_alloc_rx_mpwqe may post
UMR WQEs to ICOSQ, and with the bad timing, the wqe_info of the first
UMR may be overwritten by the wqe_info of the NOP posted by
mlx5e_activate_rq.
The consequence is that icosq->db.wqe_info[0].num_wqebbs will be changed
from MLX5E_UMR_WQEBBS to 1, disrupting the integrity of the array-based
linked list in wqe_info[]. mlx5e_poll_ico_cq will hang in an infinite
loop after processing wqe_info[0], because after the corruption, the
next item to be processed will be wqe_info[1], which is filled with
zeros, and `sqcc += wi->num_wqebbs` will never move further.
This commit fixes this race condition by using async_icosq to post the
NOP and trigger the interrupt. async_icosq is always protected with a
spinlock, eliminating the race condition.
Fixes: bc77b240b3 ("net/mlx5e: Add fragmented memory support for RX multi packet WQE")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reported-by: Karsten Nielsen <karsten@foo-bar.dk>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.