linux-kernel - Re: [PATCH v2] kdb: Make memory allocations more robust

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Message-ID: <20210122103356.pekf7wx3smknyotl@maple.lan>
Date:   Fri, 22 Jan 2021 10:33:56 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     kgdb-bugreport@...ts.sourceforge.net, jason.wessel@...driver.com,
        dianders@...omium.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kdb: Make memory allocations more robust

On Fri, Jan 22, 2021 at 03:50:50PM +0530, Sumit Garg wrote:
> Currently kdb uses in_interrupt() to determine whether it's library

Looks like a good change just a few nitpicks with the description:

s/it's/its/

> code has been called from the kgdb trap handler or from a saner calling
> context such as driver init. This approach is broken because
> in_interrupt() alone isn't able to determine kgdb trap handler entry via
> normal task context such as [1].

Why footnote this and aren't breakpoints a far more natural reason to
enter the debugger?

The following will be clearer for backporting, etc:

... detmermine kgdb trap handler entry from normal task context. This
can happen during normal use of basic features such as breakpoints
and can also be trivially reproduced using: echo g > /proc/sysrq-trigger



> 
> We can improve this by adding check for in_dbg_master() instead which
> explicitly determines if we are running in debugger context.
> 
> [1] $ echo g > /proc/sysrq-trigger
> 

Cc: stable@ ?


> Signed-off-by: Sumit Garg <sumit.garg@...aro.org>


Daniel.



> ---
> 
> Changes in v2:
> - Get rid of redundant in_atomic() check.
> 
>  kernel/debug/kdb/kdb_private.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
> index 7a4a181..344eb0d 100644
> --- a/kernel/debug/kdb/kdb_private.h
> +++ b/kernel/debug/kdb/kdb_private.h
> @@ -231,7 +231,7 @@ extern struct task_struct *kdb_curr_task(int);
>  
>  #define kdb_task_has_cpu(p) (task_curr(p))
>  
> -#define GFP_KDB (in_interrupt() ? GFP_ATOMIC : GFP_KERNEL)
> +#define GFP_KDB (in_dbg_master() ? GFP_ATOMIC : GFP_KERNEL)
>  
>  extern void *debug_kmalloc(size_t size, gfp_t flags);
>  extern void debug_kfree(void *);
> -- 
> 2.7.4
>