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5c11f7d9f8
We may send a request (with or without its data) from two paths:
1. From our I/O context nvme_tcp_io_work which is triggered from:
- queue_rq
- r2t reception
- socket data_ready and write_space callbacks
2. Directly from queue_rq if the send_list is empty (because we want to
save the context switch associated with scheduling our io_work).
However, given that now we have the send_mutex, we may run into a race
condition where none of these contexts will send the pending payload to
the controller. Both io_work send path and queue_rq send path
opportunistically attempt to acquire the send_mutex however queue_rq only
attempts to send a single request, and if io_work context fails to
acquire the send_mutex it will complete without rescheduling itself.
The race can trigger with the following sequence:
1. queue_rq sends request (no incapsule data) and blocks
2. RX path receives r2t - prepares data PDU to send, adds h2cdata PDU
to the send_list and schedules io_work
3. io_work triggers and cannot acquire the send_mutex - because of (1),
ends without self rescheduling
4. queue_rq completes the send, and completes
==> no context will send the h2cdata - timeout.
Fix this by having queue_rq sending as much as it can from the send_list
such that if it still has any left, its because the socket buffer is
full and the socket write_space callback will trigger, thus guaranteeing
that a context will be scheduled to send the h2cdata PDU.
Fixes:
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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.