Specifically, pin the stack in save_stack_trace_tsk() and show_trace_log_lvl().
This will prevent a crash if the target task dies before or while dumping its stack once we start freeing task stacks early. Cc: Josh Poimboeuf <[email protected]> Signed-off-by: Andy Lutomirski <[email protected]> --- arch/x86/kernel/dumpstack_32.c | 5 +++++ arch/x86/kernel/dumpstack_64.c | 5 +++++ arch/x86/kernel/stacktrace.c | 5 +++++ 3 files changed, 15 insertions(+) diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c index 2d65cfa5e0b4..122f37d7bb7e 100644 --- a/arch/x86/kernel/dumpstack_32.c +++ b/arch/x86/kernel/dumpstack_32.c @@ -163,6 +163,9 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs, unsigned long *stack; int i; + if (!try_get_task_stack(task)) + return; + sp = sp ? : get_stack_pointer(task, regs); stack = sp; @@ -179,6 +182,8 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs, } pr_cont("\n"); show_trace_log_lvl(task, regs, sp, bp, log_lvl); + + put_task_stack(task); } diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c index 8cb6004a4dfd..16c0d5f89b5e 100644 --- a/arch/x86/kernel/dumpstack_64.c +++ b/arch/x86/kernel/dumpstack_64.c @@ -218,6 +218,9 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs, unsigned long *stack; int i; + if (!try_get_task_stack(task)) + return; + irq_stack_end = (unsigned long *)this_cpu_read(irq_stack_ptr); irq_stack = irq_stack_end - (IRQ_STACK_SIZE / sizeof(long)); @@ -253,6 +256,8 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs, pr_cont("\n"); show_trace_log_lvl(task, regs, sp, bp, log_lvl); + + put_task_stack(task); } void show_regs(struct pt_regs *regs) diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c index 785aef1c7ef5..23fa81e24c8a 100644 --- a/arch/x86/kernel/stacktrace.c +++ b/arch/x86/kernel/stacktrace.c @@ -79,9 +79,14 @@ void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace) void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace) { + if (!try_get_task_stack(tsk)) + return; + dump_trace(tsk, NULL, NULL, 0, &save_stack_ops_nosched, trace); if (trace->nr_entries < trace->max_entries) trace->entries[trace->nr_entries++] = ULONG_MAX; + + put_task_stack(tsk); } EXPORT_SYMBOL_GPL(save_stack_trace_tsk); -- 2.7.4
