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.
Deadlock 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);
[[against next-20160929]]
v2:
-- fix build error on !NMI configs, reported by Fengguang
-- reworked the series based on Petr's feedback
-- added a new patch to drop zap_locks()
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: use alternative printk buffers
printk: report printk recursion from alt_printk flush
printk: remove zap_locks() function
include/linux/printk.h | 21 +++-
init/Kconfig | 16 +--
init/main.c | 2 +-
kernel/kexec_core.c | 2 +-
kernel/panic.c | 4 +-
kernel/printk/Makefile | 2 +-
kernel/printk/{nmi.c => alt_printk.c} | 207 +++++++++++++++++++++++++---------
kernel/printk/internal.h | 44 ++++----
kernel/printk/printk.c | 92 +++------------
lib/nmi_backtrace.c | 2 +-
10 files changed, 220 insertions(+), 172 deletions(-)
rename kernel/printk/{nmi.c => alt_printk.c} (58%)
--
2.10.0.372.g6fe1b14
