b888a5f713
Commit67ec1072b0("ALSA: pcm: Fix rwsem deadlock for non-atomic PCM stream") fixes deadlock for non-atomic PCM stream. But, This patch causes antother stuck. If writer is RT thread and reader is a normal thread, the reader thread will be difficult to get scheduled. It may not give chance to release readlocks and writer gets stuck for a long time if they are pinned to single cpu. The deadlock described in the previous commit is because the linux rwsem queues like a FIFO. So, we might need non-FIFO writelock, not non-block one. My suggestion is that the writer gives reader a chance to be scheduled by using the minimum msleep() instaed of spinning without blocking by writer. Also, The *_nonblock may be changed to *_nonfifo appropriately to this concept. In terms of performance, when trylock is failed, this minimum periodic msleep will have the same performance as the tick-based schedule()/wake_up_q(). [ Although this has a fairly high performance penalty, the relevant code path became already rare due to the previous commit ("ALSA: pcm: Call snd_pcm_unlink() conditionally at closing"). That is, now this unconditional msleep appears only when using linked streams, and this must be a rare case. So we accept this as a quick workaround until finding a more suitable one -- tiwai ] Fixes:67ec1072b0("ALSA: pcm: Fix rwsem deadlock for non-atomic PCM stream") Suggested-by: Wonmin Jung <wonmin.jung@lge.com> Signed-off-by: Chanho Min <chanho.min@lge.com> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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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.