From: Michael Ellerman Date: Fri, 28 Mar 2008 08:11:48 +0000 (+1100) Subject: [POWERPC] Fix missed hardware breakpoints across multiple threads X-Git-Tag: v2.6.25-rc8~67^2 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a2ceff5e555e664751bc653a4d9b133efa18c742;p=linux-2.6 [POWERPC] Fix missed hardware breakpoints across multiple threads There is a bug in the powerpc DABR (data access breakpoint) handling, which can result in us missing breakpoints if several threads are trying to break on the same address. The circumstances are that do_page_fault() calls do_dabr(), this clears the DABR (sets it to 0) and sets up the signal which will report to userspace that the DABR was hit. The do_signal() code will restore the DABR value on the way out to userspace. If we reschedule before calling do_signal(), __switch_to() will check the cached DABR value and compare it to the new thread's value, if they match we don't set the DABR in hardware. So if two threads have the same DABR value, and we schedule from one to the other after taking the interrupt for the first thread hitting the DABR, the second thread will run without the DABR set in hardware. The cleanest fix is to move the cache update into set_dabr(), that way we can't forget to do it. Reported-by: Jan Kratochvil Signed-off-by: Michael Ellerman Signed-off-by: Paul Mackerras --- diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 59311ec0d4..4ec6055215 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -241,8 +241,12 @@ void discard_lazy_cpu_state(void) } #endif /* CONFIG_SMP */ +static DEFINE_PER_CPU(unsigned long, current_dabr); + int set_dabr(unsigned long dabr) { + __get_cpu_var(current_dabr) = dabr; + #ifdef CONFIG_PPC_MERGE /* XXX for now */ if (ppc_md.set_dabr) return ppc_md.set_dabr(dabr); @@ -259,8 +263,6 @@ int set_dabr(unsigned long dabr) DEFINE_PER_CPU(struct cpu_usage, cpu_usage_array); #endif -static DEFINE_PER_CPU(unsigned long, current_dabr); - struct task_struct *__switch_to(struct task_struct *prev, struct task_struct *new) { @@ -325,10 +327,8 @@ struct task_struct *__switch_to(struct task_struct *prev, #endif /* CONFIG_SMP */ - if (unlikely(__get_cpu_var(current_dabr) != new->thread.dabr)) { + if (unlikely(__get_cpu_var(current_dabr) != new->thread.dabr)) set_dabr(new->thread.dabr); - __get_cpu_var(current_dabr) = new->thread.dabr; - } new_thread = &new->thread; old_thread = ¤t->thread;