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

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Message-Id: <1611308311-2530-1-git-send-email-sumit.garg@linaro.org>
Date:   Fri, 22 Jan 2021 15:08:31 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     kgdb-bugreport@...ts.sourceforge.net
Cc:     jason.wessel@...driver.com, daniel.thompson@...aro.org,
        dianders@...omium.org, linux-kernel@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>
Subject: [PATCH] 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() which explicitly
determines if we are running in debugger context. Also, use in_atomic()
instead of in_interrupt() as the former is more appropriate to know atomic
context and moreover the later one is deprecated.

[1] $ echo g > /proc/sysrq-trigger

Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
---
 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..7a9ebd9 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_atomic() || 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