On Tue 2016-10-18 19:08:31, Peter Zijlstra wrote:
> Some people figured vprintk_emit() makes for a nice API and exported
> it, bypassing the kdb trap.
I think that nobody saw this problem because kdb_trap_printk was
used only for a limited number of printk's. It is just a trick
how to use generic functions to print messages in the kdb context,
e.g. for getting backtraces.
But the patch makes sense.
> This still leaves vprintk_nmi() outside of the kbd reach, should that
> be fixed too?
It is perfectly fine. Messages from NMI context are not meant for
kdb anyway.
> Cc: Jason Wessel <jason.wes...@windriver.com>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> ---
> kernel/printk/printk.c | 19 ++++++++-----------
> 1 file changed, 8 insertions(+), 11 deletions(-)
>
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1750,6 +1750,13 @@ asmlinkage int vprintk_emit(int facility
> /* cpu currently holding logbuf_lock in this function */
> static unsigned int logbuf_cpu = UINT_MAX;
>
> +#ifdef CONFIG_KGDB_KDB
> + if (unlikely(kdb_trap_printk)) {
> + r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
> + return r;
r is not defined. It is fixed in the next patch but it breaks
bisectability.
Please, find below an updated patch that also includes
my Reviewed-by.
>From 5adf18de45ba986ea3ae611446828238f4d65fe0 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <pet...@infradead.org>
Date: Tue, 18 Oct 2016 19:08:31 +0200
Subject: [PATCH 1/3] printk: Fix kdb_trap_printk placement
Some people figured vprintk_emit() makes for a nice API and exported
it, bypassing the kdb trap.
This still leaves vprintk_nmi() outside of the kbd reach, should that
be fixed too?
Cc: Jason Wessel <jason.wes...@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
Reviewed-by: Petr Mladek <pmla...@suse.com>
---
kernel/printk/printk.c | 17 ++++++-----------
1 file changed, 6 insertions(+), 11 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f7a55e9ff2f7..541ce7705353 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1781,6 +1781,11 @@ asmlinkage int vprintk_emit(int facility, int level,
/* cpu currently holding logbuf_lock in this function */
static unsigned int logbuf_cpu = UINT_MAX;
+#ifdef CONFIG_KGDB_KDB
+ if (unlikely(kdb_trap_printk))
+ return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
+#endif
+
if (level == LOGLEVEL_SCHED) {
level = LOGLEVEL_DEFAULT;
in_sched = true;
@@ -1923,17 +1928,7 @@ asmlinkage int printk_emit(int facility, int level,
int vprintk_default(const char *fmt, va_list args)
{
- int r;
-
-#ifdef CONFIG_KGDB_KDB
- if (unlikely(kdb_trap_printk)) {
- r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
- return r;
- }
-#endif
- r = vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
-
- return r;
+ return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
}
EXPORT_SYMBOL_GPL(vprintk_default);
--
1.8.5.6
