Petr Mladek 42a0bb3f71 printk/nmi: generic solution for safe printk in NMI ... printk() takes some locks and could not be used a safe way in NMI context. The chance of a deadlock is real especially when printing stacks from all CPUs. This particular problem has been addressed on x86 by the commit a9edc88093 ("x86/nmi: Perform a safe NMI stack trace on all CPUs"). The patchset brings two big advantages. First, it makes the NMI backtraces safe on all architectures for free. Second, it makes all NMI messages almost safe on all architectures (the temporary buffer is limited. We still should keep the number of messages in NMI context at minimum). Note that there already are several messages printed in NMI context: WARN_ON(in_nmi()), BUG_ON(in_nmi()), anything being printed out from MCE handlers. These are not easy to avoid. This patch reuses most of the code and makes it generic. It is useful for all messages and architectures that support NMI. The alternative printk_func is set when entering and is reseted when leaving NMI context. It queues IRQ work to copy the messages into the main ring buffer in a safe context. __printk_nmi_flush() copies all available messages and reset the buffer. Then we could use a simple cmpxchg operations to get synchronized with writers. There is also used a spinlock to get synchronized with other flushers. We do not longer use seq_buf because it depends on external lock. It would be hard to make all supported operations safe for a lockless use. It would be confusing and error prone to make only some operations safe. The code is put into separate printk/nmi.c as suggested by Steven Rostedt. It needs a per-CPU buffer and is compiled only on architectures that call nmi_enter(). This is achieved by the new HAVE_NMI Kconfig flag. The are MN10300 and Xtensa architectures. We need to clean up NMI handling there first. Let's do it separately. The patch is heavily based on the draft from Peter Zijlstra, see https://lkml.org/lkml/2015/6/10/327 [arnd@arndb.de: printk-nmi: use %zu format string for size_t] [akpm@linux-foundation.org: min_t->min - all types are size_t here] Signed-off-by: Petr Mladek <pmladek@suse.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Steven Rostedt <rostedt@goodmis.org> Cc: Jan Kara <jack@suse.cz> Acked-by: Russell King <rmk+kernel@arm.linux.org.uk> [arm part] Cc: Daniel Thompson <daniel.thompson@linaro.org> Cc: Jiri Kosina <jkosina@suse.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: David Miller <davem@davemloft.net> Cc: Daniel Thompson <daniel.thompson@linaro.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2016-05-20 17:58:30 -07:00
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boards	This is the bulk of GPIO changes for kernel cycle v4.7:	2016-05-17 17:39:42 -07:00
boot	sh: Disable trace for kernel uncompressing.	2016-03-17 19:45:38 +00:00
cchips	genirq: Remove irq argument from irq flow handlers	2015-09-16 15:47:51 +02:00
configs	PM: Eliminate CONFIG_PM_RUNTIME	2014-12-19 22:55:06 +01:00
drivers	PCI: Remove unused "pci_probe" flags	2015-07-27 17:09:40 -05:00
include	Merge branch 'locking-rwsem-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2016-05-16 13:41:02 -07:00
kernel	exit_thread: accept a task parameter to be exited	2016-05-20 17:58:30 -07:00
lib	sh: New gcc support	2016-03-17 19:45:44 +00:00
lib64	sh64: Kill off old exception debugging helpers.	2012-06-14 14:12:18 +09:00
math-emu	sh: remove unused do_fpu_error	2014-04-03 16:20:52 -07:00
mm	Merge branch 'mm-pkeys-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2016-03-20 19:08:56 -07:00
oprofile	oprofile, arm/sh: Fix oprofile_arch_exit() linkage issue	2011-12-23 11:58:34 +01:00
tools	sh: Add RSK2+SH7269 board	2012-05-10 17:20:01 +09:00
Kconfig	printk/nmi: generic solution for safe printk in NMI	2016-05-20 17:58:30 -07:00
Kconfig.cpu	arch/sh: remove depends on CONFIG_EXPERIMENTAL	2013-01-21 14:43:13 -08:00
Kconfig.debug	sh: dwarf unwinder depends on SHcompact.	2012-03-30 19:31:22 +09:00
Makefile	sh: also try passing -m4-nofpu for SH2A builds	2014-07-23 15:10:54 -07:00