[RFC][PATCH v2 0/2] printk: Make printk() completely async

From: Sergey Senozhatsky
Date: Sat Mar 05 2016 - 05:58:00 EST


Hello,

RFC

The patch set is a slightly updated Jan Kara's patches. The majority
of the changes are in 0001 (described below in details).

I've performed some tests and haven't spotted any problems, I'll
certainly do more tests. Any feedback is appreciated.

I had additional patches on top of the series, but I decided not to post
them. I'm unhappy with console semaphore, this must be a separate mail
loop and a patch set, some day.


The patch set is against next-20160304 with reverted NMI patches.


v2 (Sergey):
- use dedicated printk workqueue with WQ_MEM_RECLAIM bit
- fallback to system-wide workqueue only if allocation of printk_wq has
failed
- do not use system_wq as a fallback wq. both console_lock() and onsole_unlock()
can spend a significant amount of time; so we need to use system_long_wq.
- rework sync/!sync detection logic
a) we can have deferred (in_sched) messages before we allocate printk_wq,
so the only way to handle those messages is via IRQ context
b) even in printk.synchronous mode, deferred messages must not be printed
directly, and should go via IRQ context
c) even if we allocated printk_wq and have !sync_printk mode, we must route
deferred messages via IRQ context
- so this adds additional bool flags to vprint_emit() and introduces a new
pending bit to `printk_pending'
- fix build on !PRINTK configs

Jan Kara (2):
printk: Make printk() completely async
printk: Skip messages on oops

Documentation/kernel-parameters.txt | 10 ++
kernel/printk/printk.c | 230 +++++++++++++++++++++++++++---------
2 files changed, 181 insertions(+), 59 deletions(-)

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2.8.0.rc0