Messages in this thread | | | From | Sergey Senozhatsky <> | Subject | [RFC][PATCHv4 0/6] printk: use printk_safe to handle printk() recursive calls | Date | Fri, 28 Oct 2016 00:49:27 +0900 |
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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 printk_safe 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);
e) printk from console_cont_flush() /*and down the call chain */ printk() console_unlock() call_console_drivers() ... WARN_ON(1);
[[against next-20161027]]
v4: -- addressed Steven's review points -- use printk_safe in console_cont_flush()
v3: (review by Petr) -- renamed to printk_safe -- !NMI config build fix -- report lost messages for both printk_sae and printk_nmi -- dropped recursion reporting patch -- etc.
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 (6): printk: use vprintk_func in vprintk() printk: rename nmi.c and exported api printk: introduce per-cpu safe_print seq buffer printk: report lost messages in printk safe/nmi contexts printk: use printk_safe buffers printk: remove zap_locks() function
arch/arm/kernel/smp.c | 4 +- include/linux/hardirq.h | 4 +- include/linux/printk.h | 29 ++-- init/Kconfig | 16 ++- init/main.c | 2 +- kernel/kexec_core.c | 2 +- kernel/panic.c | 4 +- kernel/printk/Makefile | 2 +- kernel/printk/internal.h | 63 ++++----- kernel/printk/printk.c | 124 +++++------------- kernel/printk/{nmi.c => printk_safe.c} | 233 +++++++++++++++++++++++++-------- lib/nmi_backtrace.c | 2 +- 12 files changed, 274 insertions(+), 211 deletions(-) rename kernel/printk/{nmi.c => printk_safe.c} (54%)
-- 2.10.1.502.g6598894
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