2021-01-22 10:36:40

by Sumit Garg

Subject: [PATCH v2] kdb: Make memory allocations more robust

Currently kdb uses in_interrupt() to determine whether it's library
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].

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

Signed-off-by: Sumit Garg <[email protected]>
---

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

2021-01-22 10:39:59

by Daniel Thompson

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 <[email protected]>


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
>