From: Steven Rostedt <rostedt@goodmis.org>
To: Petr Mladek <pmladek@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Russell King <rmk+kernel@arm.linux.org.uk>,
Daniel Thompson <daniel.thompson@linaro.org>,
Jiri Kosina <jkosina@suse.com>, Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Chris Metcalf <cmetcalf@ezchip.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-arm-kernel@lists.infradead.org,
adi-buildroot-devel@lists.sourceforge.net,
linux-cris-kernel@axis.com, linux-mips@linux-mips.org,
linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
Jan Kara <jack@suse.cz>, Ralf Baechle <ralf@linux-mips.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
David Miller <davem@davemloft.net>
Subject: Re: [PATCH v5 1/4] printk/nmi: generic solution for safe printk in NMI
Date: Wed, 19 Apr 2017 13:13:41 -0400 [thread overview]
Message-ID: <20170419131341.76bc7634@gandalf.local.home> (raw)
In-Reply-To: <1461239325-22779-2-git-send-email-pmladek@suse.com>
On Thu, 21 Apr 2016 13:48:42 +0200
Petr Mladek <pmladek@suse.com> wrote:
> printk() takes some locks and could not be used a safe way in NMI context.
I just found a problem with this solution. It kills ftrace dumps from
NMI context :-(
[ 1295.168495] <...>-67423 10dNh1 382171111us : do_raw_spin_lock <-_raw_spin_lock
[ 1295.168495] <...>-67423 10dNh1 382171111us : sched_stat_runtime: comm=cc1 pid=67423 runtime=96858 [ns] vruntime=11924198270 [ns]
[ 1295.168496] <...>-67423 10dNh1 382171111us : lock_acquire: ffffffff81c5c940 read rcu_read_lock
[ 1295.168497]
[ 1295.168498] Lost 4890096 message(s)!
[ 1296.805063] ---[ end Kernel panic - not syncing: Hard LOCKUP
[ 1296.811553] unchecked MSR access error: WRMSR to 0x83f (tried to write 0x00000000000000f6) at rIP: 0xffffffff81046fc7 (native_apic_msr_write+0x27/0x40)
[ 1296.811553] Call Trace:
[ 1296.811553] <NMI>
I was hoping to see a cause of a hard lockup by enabling
ftrace_dump_on_oops. But as NMIs now have a very small buffer that
gets flushed, we need to find a new way to print out the full ftrace
buffer over serial.
Thoughts?
-- Steve
>
> 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
> a9edc8809328 ("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>
> Cc: Russell King <rmk+kernel@arm.linux.org.uk>
> 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>
next prev parent reply other threads:[~2017-04-19 17:13 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-21 11:48 [PATCH v5 0/4] Cleaning printk stuff in NMI context Petr Mladek
2016-04-21 11:48 ` [PATCH v5 1/4] printk/nmi: generic solution for safe printk in NMI Petr Mladek
2016-04-27 9:31 ` Russell King - ARM Linux
2017-04-19 17:13 ` Steven Rostedt [this message]
2017-04-19 17:21 ` Peter Zijlstra
2017-04-20 3:31 ` Sergey Senozhatsky
2017-04-20 13:11 ` Petr Mladek
2017-04-21 1:57 ` Sergey Senozhatsky
2017-04-21 12:06 ` Petr Mladek
2017-04-24 2:17 ` Sergey Senozhatsky
2017-04-27 13:38 ` Petr Mladek
2017-04-27 14:31 ` Steven Rostedt
2017-04-27 15:28 ` Petr Mladek
2017-04-27 15:42 ` Steven Rostedt
2017-04-28 9:02 ` Peter Zijlstra
2017-04-28 13:44 ` Petr Mladek
2017-04-28 13:58 ` Peter Zijlstra
2017-04-28 14:47 ` Steven Rostedt
2017-04-27 16:14 ` Steven Rostedt
2017-04-28 1:35 ` Sergey Senozhatsky
2017-04-28 12:57 ` Petr Mladek
2017-04-28 14:16 ` Steven Rostedt
2017-04-28 1:25 ` Sergey Senozhatsky
2017-04-28 12:38 ` Petr Mladek
2016-04-21 11:48 ` [PATCH v5 2/4] printk/nmi: warn when some message has been lost in NMI context Petr Mladek
2016-04-27 9:34 ` Russell King - ARM Linux
2016-04-21 11:48 ` [PATCH v5 3/4] printk/nmi: increase the size of NMI buffer and make it configurable Petr Mladek
2016-04-21 11:48 ` [PATCH v5 4/4] printk/nmi: flush NMI messages on the system panic Petr Mladek
2016-04-23 3:49 ` Sergey Senozhatsky
2016-04-26 14:21 ` Petr Mladek
2016-04-27 0:34 ` Sergey Senozhatsky
2016-04-27 0:36 ` [PATCH v5 0/4] Cleaning printk stuff in NMI context Sergey Senozhatsky
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170419131341.76bc7634@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=adi-buildroot-devel@lists.sourceforge.net \
--cc=akpm@linux-foundation.org \
--cc=benh@kernel.crashing.org \
--cc=cmetcalf@ezchip.com \
--cc=daniel.thompson@linaro.org \
--cc=davem@davemloft.net \
--cc=jack@suse.cz \
--cc=jkosina@suse.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-cris-kernel@axis.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@linux-mips.org \
--cc=linux-s390@vger.kernel.org \
--cc=linux-sh@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=pmladek@suse.com \
--cc=ralf@linux-mips.org \
--cc=rmk+kernel@arm.linux.org.uk \
--cc=schwidefsky@de.ibm.com \
--cc=sergey.senozhatsky.work@gmail.com \
--cc=sparclinux@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).