Messages in this thread Patch in this message | | | Date | Wed, 20 May 2020 12:22:33 +0200 | From | Petr Mladek <> | Subject | [PATCH v2] printk/kdb: Redirect printk messages into kdb in any context |
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kdb has to get messages on consoles even when the system is stopped. It uses kdb_printf() internally and calls console drivers on its own.
It uses a hack to reuse an existing code. It sets "kdb_trap_printk" global variable to redirect even the normal printk() into the kdb_printf() variant.
The variable "kdb_trap_printk" is checked in printk_default() and it is ignored when printk is redirected to printk_safe in NMI context. Solve this by moving the check into printk_func().
It is obvious that it is not fully safe. But it does not make things worse. The console drivers are already called in this context by db_printf() direct calls.
Reported-by: Sumit Garg <sumit.garg@linaro.org> Tested-by: Sumit Garg <sumit.garg@linaro.org> Signed-off-by: Petr Mladek <pmladek@suse.com> --- Changes in v2:
+ more detailed commit message
kernel/printk/printk.c | 14 +------------- kernel/printk/printk_safe.c | 7 +++++++ 2 files changed, 8 insertions(+), 13 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 9a9b6156270b..63a1aa377cd9 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -35,7 +35,6 @@ #include <linux/memblock.h> #include <linux/syscalls.h> #include <linux/crash_core.h> -#include <linux/kdb.h> #include <linux/ratelimit.h> #include <linux/kmsg_dump.h> #include <linux/syslog.h> @@ -2036,18 +2035,7 @@ EXPORT_SYMBOL(vprintk); int vprintk_default(const char *fmt, va_list args) { - int r; - -#ifdef CONFIG_KGDB_KDB - /* Allow to pass printk() to kdb but avoid a recursion. */ - if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0)) { - 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); diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index d9a659a686f3..7ccb821d0bfe 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -6,6 +6,7 @@ #include <linux/preempt.h> #include <linux/spinlock.h> #include <linux/debug_locks.h> +#include <linux/kdb.h> #include <linux/smp.h> #include <linux/cpumask.h> #include <linux/irq_work.h> @@ -359,6 +360,12 @@ void __printk_safe_exit(void) __printf(1, 0) int vprintk_func(const char *fmt, va_list args) { +#ifdef CONFIG_KGDB_KDB + /* Allow to pass printk() to kdb but avoid a recursion. */ + if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0)) + return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args); +#endif + /* * Try to use the main logbuf even in NMI. But avoid calling console * drivers that might have their own locks. -- 2.26.1
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