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Douglas Anderson
3d9319c27c
This reverts commit5c7e105cd1. As identified by KASAN, the simplification done by the cleanup patch was not legal. >From tracing through the code, it can be seen that we're transmitting from a 4096-byte circular buffer. We copy anywhere from 1-4 bytes from it each time. The simplification runs into trouble when we get near the end of the circular buffer. For instance, we might start out with xmit->tail = 4094 and we want to transfer 4 bytes. With the code before simplification this was no problem. We'd read buf[4094], buf[4095], buf[0], and buf[1]. With the new code we'll do a memcpy(&buf[4094], 4) which reads 2 bytes past the end of the buffer and then skips transmitting what's at buf[0] and buf[1]. KASAN isn't 100% consistent at reporting this for me, but to be extra confident in the analysis, I added traces of the tail and tx_bytes and then wrote a test program: while true; do echo -n "abcdefghijklmnopqrstuvwxyz0" > /dev/ttyMSM0 sleep .1 done I watched the traces over SSH and saw: qcom_geni_serial_send_chunk_fifo: 4093 4 qcom_geni_serial_send_chunk_fifo: 1 3 Which indicated that one byte should be missing. Sure enough the output that should have been: abcdefghijklmnopqrstuvwxyz0 In one case was actually missing a byte: abcdefghijklmnopqrstuvwyz0 Running "ls -al" on large directories also made the missing bytes obvious since columns didn't line up. While the original code may not be the most elegant, we only talking about copying up to 4 bytes here. Let's just go back to the code that worked. Fixes:5c7e105cd1("tty: serial: simplify qcom_geni_serial_send_chunk_fifo()") Cc: stable <[email protected]> Signed-off-by: Douglas Anderson <[email protected]> Acked-by: Jiri Slaby <[email protected]> Tested-by: Johan Hovold <[email protected]> Link: https://lore.kernel.org/r/20240304174952.1.I920a314049b345efd1f69d708e7f74d2213d0b49@changeid Signed-off-by: Greg Kroah-Hartman <[email protected]>
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.