From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jiri Kosina <jkosina@suse.cz>, Michal Hocko <mhocko@suse.cz>,
Jan Kara <jack@suse.cz>, Frederic Weisbecker <fweisbec@gmail.com>,
Dave Anderson <anderson@redhat.com>,
Petr Mladek <pmladek@suse.cz>
Subject: Re: [RFC][PATCH 2/3] printk: Add per_cpu printk func to allow printk to be diverted
Date: Mon, 23 Jun 2014 09:06:01 -0700 [thread overview]
Message-ID: <20140623160601.GA23817@linux.vnet.ibm.com> (raw)
In-Reply-To: <20140619213952.209176403@goodmis.org>
On Thu, Jun 19, 2014 at 05:33:31PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
>
> Being able to divert printk to call another function besides the normal
> logging is useful for such things like NMI handling. If some functions
> are to be called from NMI that does printk() it is possible to lock up
> the box if the nmi handler triggers when another printk is happening.
>
> One example of this use is to perform a stack trace on all CPUs via NMI.
> But if the NMI is to do the printk() it can cause the system to lock up.
> By allowing the printk to be diverted to another function that can safely
> record the printk output and then print it when it in a safe context
> then NMIs will be safe to call these functions like show_regs().
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> include/linux/percpu.h | 3 +++
> include/linux/printk.h | 2 ++
> kernel/printk/printk.c | 38 +++++++++++++++++++++++++++++---------
> 3 files changed, 34 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/percpu.h b/include/linux/percpu.h
> index 8419053d0f2e..9997c92ce3bd 100644
> --- a/include/linux/percpu.h
> +++ b/include/linux/percpu.h
> @@ -802,4 +802,7 @@ do { __this_cpu_preempt_check("or"); \
> (__this_cpu_preempt_check("cmpxchg_double"),__pcpu_double_call_return_bool(raw_cpu_cmpxchg_double_, (pcp1), (pcp2), (oval1), (oval2), (nval1), (nval2)))
> #endif
>
> +/* To avoid include hell, as printk can not declare this, we declare it here */
> +DECLARE_PER_CPU(printk_func_t, printk_func);
> +
> #endif /* __LINUX_PERCPU_H */
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index 319ff7e53efb..e26310b2d2fd 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -159,6 +159,8 @@ extern int kptr_restrict;
>
> extern void wake_up_klogd(void);
>
> +typedef int(*printk_func_t)(const char *fmt, va_list args);
> +
> void log_buf_kexec_setup(void);
> void __init setup_log_buf(int early);
> void dump_stack_set_arch_desc(const char *fmt, ...);
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index ea2d5f6962ed..d019ccd10d4c 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1764,6 +1764,30 @@ asmlinkage int printk_emit(int facility, int level,
> }
> EXPORT_SYMBOL(printk_emit);
>
> +int vprintk_default(const char *fmt, va_list args)
> +{
> + int r;
> +
> +#ifdef CONFIG_KGDB_KDB
> + if (unlikely(kdb_trap_printk)) {
> + r = vkdb_printf(fmt, args);
> + return r;
> + }
> +#endif
> + r = vprintk_emit(0, -1, NULL, 0, fmt, args);
> +
> + return r;
> +}
> +EXPORT_SYMBOL_GPL(vprintk_default);
> +
> +/*
> + * This allows printk to be diverted to another function per cpu.
> + * This is useful for calling printk functions from within NMI
> + * without worrying about race conditions that can lock up the
> + * box.
> + */
> +DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default;
> +
> /**
> * printk - print a kernel message
> * @fmt: format string
> @@ -1787,19 +1811,15 @@ EXPORT_SYMBOL(printk_emit);
> */
> asmlinkage __visible int printk(const char *fmt, ...)
> {
> + printk_func_t vprintk_func;
> va_list args;
> int r;
>
> -#ifdef CONFIG_KGDB_KDB
> - if (unlikely(kdb_trap_printk)) {
> - va_start(args, fmt);
> - r = vkdb_printf(fmt, args);
> - va_end(args);
> - return r;
> - }
> -#endif
> va_start(args, fmt);
> - r = vprintk_emit(0, -1, NULL, 0, fmt, args);
> + preempt_disable();
> + vprintk_func = this_cpu_read(printk_func);
> + r = vprintk_func(fmt, args);
> + preempt_enable();
> va_end(args);
>
> return r;
> --
> 2.0.0.rc2
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
next prev parent reply other threads:[~2014-06-23 16:06 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-19 21:33 [RFC][PATCH 0/3] x86/nmi: Print all cpu stacks from NMI safely Steven Rostedt
2014-06-19 21:33 ` [RFC][PATCH 1/3] trace_seq: Move the trace_seq code to lib/ Steven Rostedt
2014-06-20 4:45 ` Linus Torvalds
2014-06-20 16:21 ` Steven Rostedt
2014-06-20 5:06 ` Andrew Morton
2014-06-20 16:58 ` Steven Rostedt
2014-06-20 17:12 ` Andrew Morton
2014-06-20 17:17 ` Steven Rostedt
2014-06-20 20:28 ` Steven Rostedt
2014-06-20 20:51 ` Steven Rostedt
2014-06-23 16:33 ` Petr Mládek
2014-06-23 17:03 ` Steven Rostedt
2014-06-22 7:38 ` Johannes Berg
2014-06-23 16:08 ` Steven Rostedt
2014-06-23 17:38 ` Johannes Berg
2014-06-23 18:04 ` Steven Rostedt
2014-06-24 8:19 ` Johannes Berg
2014-06-19 21:33 ` [RFC][PATCH 2/3] printk: Add per_cpu printk func to allow printk to be diverted Steven Rostedt
2014-06-23 16:06 ` Paul E. McKenney [this message]
2014-06-19 21:33 ` [RFC][PATCH 3/3] x86/nmi: Perform a safe NMI stack trace on all CPUs Steven Rostedt
2014-06-20 13:58 ` Don Zickus
2014-06-20 14:21 ` Steven Rostedt
2014-06-20 14:55 ` Petr Mládek
2014-06-20 15:17 ` Steven Rostedt
2014-06-23 16:12 ` Paul E. McKenney
2014-06-19 21:56 ` [RFC][PATCH 0/3] x86/nmi: Print all cpu stacks from NMI safely Jiri Kosina
2014-06-19 22:58 ` Steven Rostedt
2014-06-19 23:03 ` Jiri Kosina
2014-06-19 23:19 ` Steven Rostedt
2014-06-19 23:27 ` Jiri Kosina
2014-06-19 23:36 ` Steven Rostedt
2014-06-19 23:38 ` Jiri Kosina
2014-06-20 14:35 ` Petr Mládek
2014-06-24 13:32 ` Konstantin Khlebnikov
2014-06-25 10:01 ` Jiri Kosina
2014-06-25 11:04 ` Konstantin Khlebnikov
2014-06-25 11:57 ` Petr Mládek
2014-06-25 12:21 ` Petr Mládek
2014-11-19 4:39 [RFC][PATCH 0/3] printk/seq-buf/NMI: Revisit of safe NMI printing with seq_buf code Steven Rostedt
2014-11-19 4:39 ` [RFC][PATCH 2/3] printk: Add per_cpu printk func to allow printk to be diverted Steven Rostedt
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=20140623160601.GA23817@linux.vnet.ibm.com \
--to=paulmck@linux.vnet.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=anderson@redhat.com \
--cc=fweisbec@gmail.com \
--cc=jack@suse.cz \
--cc=jkosina@suse.cz \
--cc=linux-kernel@vger.kernel.org \
--cc=mhocko@suse.cz \
--cc=mingo@kernel.org \
--cc=pmladek@suse.cz \
--cc=rostedt@goodmis.org \
--cc=torvalds@linux-foundation.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).