linux-kernel - Re: [PATCH 4/4] ppc64 ftrace recursion protection

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Message-ID: <20150603132214.GE19424@lst.de>
Date:	Wed, 3 Jun 2015 15:22:14 +0200
From:	Torsten Duwe <duwe@....de>
To:	Michael Ellerman <mpe@...erman.id.au>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] ppc64 ftrace recursion protection

As suggested by You and Jikos, a flag in task_struct's trace_recursion
is used to block a tracer function to recurse into itself, especially
on a data access fault. This should catch all functions called by the
fault handlers which are not yet attributed notrace.

Signed-off-by: Torsten Duwe <duwe@...e.de>

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 4717859..ae10752 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -72,6 +72,7 @@ int main(void)
 	DEFINE(THREAD, offsetof(struct task_struct, thread));
 	DEFINE(MM, offsetof(struct task_struct, mm));
 	DEFINE(MMCONTEXTID, offsetof(struct mm_struct, context.id));
+	DEFINE(TASK_TRACEREC, offsetof(struct task_struct, trace_recursion));
 #ifdef CONFIG_PPC64
 	DEFINE(AUDITCONTEXT, offsetof(struct task_struct, audit_context));
 	DEFINE(SIGSEGV, SIGSEGV);
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index a4132ef..4768104 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -1202,7 +1202,13 @@ _GLOBAL(ftrace_caller)
 	SAVE_8GPRS(16,r1)
 	SAVE_8GPRS(24,r1)
 
-
+	ld	r3, PACACURRENT(r13)
+	ld	r4, TASK_TRACEREC(r3)
+	andi.	r5, r4, 0x0010 // ( 1 << TRACE_FTRACE_BIT )
+	ori	r4, r4, 0x0010
+	std	r4, TASK_TRACEREC(r3)
+	bne	3f		// ftrace in progress - avoid recursion!
+	
 	LOAD_REG_IMMEDIATE(r3,function_trace_op)
 	ld	r5,0(r3)
 
@@ -1224,9 +1230,14 @@ ftrace_call:
 	bl	ftrace_stub
 	nop
 
+	ld	r3, PACACURRENT(r13)
+	ld	r4, TASK_TRACEREC(r3)
+	andi.	r4, r4, 0xffef // ~( 1 << TRACE_FTRACE_BIT )
+	std	r4, TASK_TRACEREC(r3)
+
 	ld	r3, _NIP(r1)
 	mtlr	r3
-
+3:
 	REST_8GPRS(0,r1)
 	REST_8GPRS(8,r1)
 	REST_8GPRS(16,r1)
--
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