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-rw-r--r--arch/x86/kernel/step.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 7a51498..f89cdc6 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -161,6 +161,16 @@ static void set_task_blockstep(struct task_struct *task, bool on)
{
unsigned long debugctl;
+ /*
+ * Ensure irq/preemption can't change debugctl in between.
+ * Note also that both TIF_BLOCKSTEP and debugctl should
+ * be changed atomically wrt preemption.
+ * FIXME: this means that set/clear TIF_BLOCKSTEP is simply
+ * wrong if task != current, SIGKILL can wakeup the stopped
+ * tracee and set/clear can play with the running task, this
+ * can confuse the next __switch_to_xtra().
+ */
+ local_irq_disable();
debugctl = get_debugctlmsr();
if (on) {
debugctl |= DEBUGCTLMSR_BTF;
@@ -169,7 +179,9 @@ static void set_task_blockstep(struct task_struct *task, bool on)
debugctl &= ~DEBUGCTLMSR_BTF;
clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
}
- update_debugctlmsr(debugctl);
+ if (task == current)
+ update_debugctlmsr(debugctl);
+ local_irq_enable();
}
/*