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-rw-r--r--arch/x86/kernel/step.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index cd3b2438a980..9b4d51d0c0d0 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -165,10 +165,11 @@ void set_task_blockstep(struct task_struct *task, bool on)
* 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().
+ *
+ * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if
+ * task is current or it can't be running, otherwise we can race
+ * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but
+ * PTRACE_KILL is not safe.
*/
local_irq_disable();
debugctl = get_debugctlmsr();