mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-14 10:02:33 -04:00
c8995932db
qemu-system-m68k -M q800 has an old bug that causes the kernel to
occasionally complain about a soft lockup:
watchdog: BUG: soft lockup - CPU#0 stuck for 5107s!
There isn't any actual lockup. The via1 clocksource produced a large
jump in jiffies, causing the watchdog to detect a stale timestamp.
The 32-bit clocksource counter runs at 783360 Hz and its period is
about 5482 seconds. Applying the "nanosecond" approximation used in
get_timestamp() in kernel/watchdog.c then yields the duration reported
in the log message above (always 5107 or 5108 in my tests):
0xffffffff / VIA_CLOCK_FREQ * 10**9 / 2**30 = 5106.209 seconds
It is notoriously difficult to correctly emulate a MOS6522 VIA chip. So
it seems wise to document the VIA clocksource driver better, especially
those hardware behaviours which the kernel relies upon.
Cc: Joshua Thompson <funaho@jurai.org>
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/f7b4c02a1c8ed74ccceb5535d7e1e202deada8ce.1750739568.git.fthain@linux-m68k.org
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
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 reStructuredText 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.