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/hw_breakpoint.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'arch/arm/kernel/hw_breakpoint.c') diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c index d37ed3501e5..eeba3800803 100644 --- a/arch/arm/kernel/hw_breakpoint.c +++ b/arch/arm/kernel/hw_breakpoint.c @@ -24,6 +24,7 @@ #define pr_fmt(fmt) "hw-breakpoint: " fmt #include +#include #include #include #include @@ -736,14 +737,17 @@ unlock: /* * Called from either the Data Abort Handler [watchpoint] or the - * Prefetch Abort Handler [breakpoint]. + * Prefetch Abort Handler [breakpoint] with preemption disabled. */ static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr, struct pt_regs *regs) { - int ret = 1; /* Unhandled fault. */ + int ret = 0; u32 dscr; + /* We must be called with preemption disabled. */ + WARN_ON(preemptible()); + /* We only handle watchpoints and hardware breakpoints. */ ARM_DBG_READ(c1, 0, dscr); @@ -758,11 +762,15 @@ static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr, watchpoint_handler(addr, regs); break; default: - goto out; + ret = 1; /* Unhandled fault. */ } - ret = 0; -out: + /* + * Re-enable preemption after it was disabled in the + * low-level exception handling code. + */ + preempt_enable(); + return ret; } -- cgit v1.2.3-18-g5258