From 7e20269647169e7ea08a62bdc4979a3ba32e615c Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Sun, 28 Nov 2010 14:57:24 +0000 Subject: ARM: hw_breakpoint: disable preemption during debug exception handling On ARM, debug exceptions occur in the form of data or prefetch aborts. One difference is that debug exceptions require access to per-cpu banked registers and data structures which are not saved in the low-level exception code. For kernels built with CONFIG_PREEMPT, there is an unlikely scenario that the debug handler ends up running on a different CPU from the one that originally signalled the event, resulting in random data being read from the wrong registers. This patch adds a debug_entry macro to the low-level exception handling code which checks whether the taken exception is a debug exception. If it is, the preempt count for the faulting process is incremented. After the debug handler has finished, the count is decremented. Acked-by: Catalin Marinas Signed-off-by: Will Deacon --- arch/arm/kernel/entry-header.S | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'arch/arm/kernel/entry-header.S') diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S index d93f976fb389..ae9464900168 100644 --- a/arch/arm/kernel/entry-header.S +++ b/arch/arm/kernel/entry-header.S @@ -165,6 +165,25 @@ .endm #endif /* !CONFIG_THUMB2_KERNEL */ + @ + @ Debug exceptions are taken as prefetch or data aborts. + @ We must disable preemption during the handler so that + @ we can access the debug registers safely. + @ + .macro debug_entry, fsr +#if defined(CONFIG_HAVE_HW_BREAKPOINT) && defined(CONFIG_PREEMPT) + ldr r4, =0x40f @ mask out fsr.fs + and r5, r4, \fsr + cmp r5, #2 @ debug exception + bne 1f + get_thread_info r10 + ldr r6, [r10, #TI_PREEMPT] @ get preempt count + add r11, r6, #1 @ increment it + str r11, [r10, #TI_PREEMPT] +1: +#endif + .endm + /* * These are the registers used in the syscall handler, and allow us to * have in theory up to 7 arguments to a function - r0 to r6. -- cgit