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Subject[RFC][PATCH 0/7] printk: use alt_printk to handle printk() recursive calls
Date
	Hello,

RFC

This patch set extends a lock-less NMI per-cpu buffers idea to
handle recursive printk() calls. The basic mechanism is pretty much the
same -- at the beginning of a deadlock-prone section we switch to lock-less
printk callback, and return back to a default printk implementation at the
end; the messages are getting flushed to a logbuf buffer from a safer
context.

Deadlocks scenarios that alt_printk can handle:

a) printk recursion from logbuf_lock spin_lock section in printk()
printk()
raw_spin_lock(&logbuf_lock);
WARN_ON(1);
raw_spin_unlock(&logbuf_lock);

b) printk from sem->lock spin_lock section
printk()
console_trylock()
down_trylock()
raw_spin_lock_irqsave(&sem->lock, flags);
WARN_ON(1);
raw_spin_unlock_irqrestore(&sem->lock, flags);

c) printk from logbuf_lock spin_lock section in console_unlock()
printk()
console_unlock()
raw_spin_lock(&logbuf_lock);
WARN_ON(1);
raw_spin_unlock(&logbuf_lock);

d) printk from ->pi_lock from semaphore up
printk()
console_unlock()
up()
try_to_wake_up()
raw_spin_lock_irqsave(&p->pi_lock, flags);
WARN_ON(1);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);

and some other.

[[against next-20160927]]


Sergey Senozhatsky (7):
printk: use vprintk_func in vprintk()
printk: rename nmi.c and exported api
printk: introduce per-cpu alt_print seq buffer
printk: make alt_printk available when config printk set
printk: drop vprintk_func function
printk: use alternative printk buffers
printk: new printk() recursion detection

include/linux/printk.h | 14 +-
init/Kconfig | 16 +-
init/main.c | 2 +-
kernel/kexec_core.c | 2 +-
kernel/panic.c | 4 +-
kernel/printk/Makefile | 2 +-
kernel/printk/alt_printk.c | 432 +++++++++++++++++++++++++++++++++++++++++++++
kernel/printk/internal.h | 26 ++-
kernel/printk/nmi.c | 268 ----------------------------
kernel/printk/printk.c | 67 +++----
lib/nmi_backtrace.c | 2 +-
11 files changed, 495 insertions(+), 340 deletions(-)
create mode 100644 kernel/printk/alt_printk.c
delete mode 100644 kernel/printk/nmi.c

--
2.10.0.372.g6fe1b14

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