Re: A bug about system call on ARM

[Will Deacon]

On Thu, May 30, 2013 at 10:09:49AM +0100, Will Deacon wrote:
> On Thu, May 30, 2013 at 02:41:42AM +0100, Wang, Yalin wrote:
> > If you have some patch for this issue,
> > I can do the test for it .
> 
> I'll have a look at cooking something which uses an exception table entry
> to rewind the PC and retry the system call. That's simpler than directly
> injecting a user page fault from the system call path.

Ok, please can you try the following?

Will

--->8

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index bc5bc0a..855926e 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -361,6 +361,15 @@ ENTRY(vector_swi)
 	str	r8, [sp, #S_PSR]		@ Save CPSR
 	str	r0, [sp, #S_OLD_R0]		@ Save OLD_R0
 	zero_fp
+	enable_irq
+	ct_user_exit
+
+#ifdef CONFIG_ALIGNMENT_TRAP
+	ldr	ip, __cr_alignment
+	ldr	ip, [ip]
+	mcr	p15, 0, ip, c1, c0		@ update control register
+#endif
+	get_thread_info tsk
 
 	/*
 	 * Get the system call number.
@@ -375,9 +384,9 @@ ENTRY(vector_swi)
 #ifdef CONFIG_ARM_THUMB
 	tst	r8, #PSR_T_BIT
 	movne	r10, #0				@ no thumb OABI emulation
-	ldreq	r10, [lr, #-4]			@ get SWI instruction
+ USER(	ldreq	r10, [lr, #-4]		)	@ get SWI instruction
 #else
-	ldr	r10, [lr, #-4]			@ get SWI instruction
+ USER(	ldr	r10, [lr, #-4]		)	@ get SWI instruction
 #endif
 #ifdef CONFIG_CPU_ENDIAN_BE8
 	rev	r10, r10			@ little endian instruction
@@ -392,22 +401,13 @@ ENTRY(vector_swi)
 	/* Legacy ABI only, possibly thumb mode. */
 	tst	r8, #PSR_T_BIT			@ this is SPSR from save_user_regs
 	addne	scno, r7, #__NR_SYSCALL_BASE	@ put OS number in
-	ldreq	scno, [lr, #-4]
+ USER(	ldreq	scno, [lr, #-4]		)
 
 #else
 	/* Legacy ABI only. */
-	ldr	scno, [lr, #-4]			@ get SWI instruction
-#endif
-
-#ifdef CONFIG_ALIGNMENT_TRAP
-	ldr	ip, __cr_alignment
-	ldr	ip, [ip]
-	mcr	p15, 0, ip, c1, c0		@ update control register
+ USER(	ldr	scno, [lr, #-4]		)	@ get SWI instruction
 #endif
-	enable_irq
-	ct_user_exit
 
-	get_thread_info tsk
 	adr	tbl, sys_call_table		@ load syscall table pointer
 
 #if defined(CONFIG_OABI_COMPAT)
@@ -442,6 +442,18 @@ local_restart:
 	eor	r0, scno, #__NR_SYSCALL_BASE	@ put OS number back
 	bcs	arm_syscall	
 	b	sys_ni_syscall			@ not private func
+
+#if defined(CONFIG_OABI_COMPAT) || !defined(CONFIG_AEABI)
+	/*
+	 * We may have faulted trying to load the SWI instruction due to
+	 * concurrent page aging on another CPU. In this case, return
+	 * back to the swi instruction and fault the page back.
+	 */
+9001:
+	sub	lr, lr, #4
+	str	lr, [sp, #S_PC]
+	b	ret_fast_syscall
+#endif
 ENDPROC(vector_swi)
 
 	/*
--
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