[text copied from commit 9bbd4c56b0b6 ("arm64: prep stack walkers for THREAD_INFO_IN_TASK")]
When CONFIG_THREAD_INFO_IN_TASK is selected, task stacks may be freed before a task is destroyed. To account for this, the stacks are refcounted, and when manipulating the stack of another task, it is necessary to get/put the stack to ensure it isn't freed and/or re-used while we do so. This patch reworks the powerpc stack walking code to account for this. When CONFIG_THREAD_INFO_IN_TASK is not selected these perform no refcounting, and this should only be a structural change that does not affect behaviour. Acked-by: Mark Rutland <mark.rutl...@arm.com> Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr> --- arch/powerpc/kernel/process.c | 23 +++++++++++++++++++++-- arch/powerpc/kernel/stacktrace.c | 29 ++++++++++++++++++++++++++--- 2 files changed, 47 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index ce393df243aa..4ffbb677c9f5 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -2027,7 +2027,7 @@ int validate_sp(unsigned long sp, struct task_struct *p, EXPORT_SYMBOL(validate_sp); -unsigned long get_wchan(struct task_struct *p) +static unsigned long __get_wchan(struct task_struct *p) { unsigned long ip, sp; int count = 0; @@ -2053,6 +2053,20 @@ unsigned long get_wchan(struct task_struct *p) return 0; } +unsigned long get_wchan(struct task_struct *p) +{ + unsigned long ret; + + if (!try_get_task_stack(p)) + return 0; + + ret = __get_wchan(p); + + put_task_stack(p); + + return ret; +} + static int kstack_depth_to_print = CONFIG_PRINT_STACK_DEPTH; void show_stack(struct task_struct *tsk, unsigned long *stack) @@ -2067,6 +2081,9 @@ void show_stack(struct task_struct *tsk, unsigned long *stack) int curr_frame = 0; #endif + if (!try_get_task_stack(tsk)) + return; + sp = (unsigned long) stack; if (tsk == NULL) tsk = current; @@ -2081,7 +2098,7 @@ void show_stack(struct task_struct *tsk, unsigned long *stack) printk("Call Trace:\n"); do { if (!validate_sp(sp, tsk, STACK_FRAME_OVERHEAD)) - return; + break; stack = (unsigned long *) sp; newsp = stack[0]; @@ -2121,6 +2138,8 @@ void show_stack(struct task_struct *tsk, unsigned long *stack) sp = newsp; } while (count++ < kstack_depth_to_print); + + put_task_stack(tsk); } #ifdef CONFIG_PPC64 diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c index e2c50b55138f..f80e1129c0f2 100644 --- a/arch/powerpc/kernel/stacktrace.c +++ b/arch/powerpc/kernel/stacktrace.c @@ -67,12 +67,17 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace) { unsigned long sp; + if (!try_get_task_stack(tsk)) + return; + if (tsk == current) sp = current_stack_pointer(); else sp = tsk->thread.ksp; save_context_stack(trace, sp, tsk, 0); + + put_task_stack(tsk); } EXPORT_SYMBOL_GPL(save_stack_trace_tsk); @@ -84,9 +89,8 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace) EXPORT_SYMBOL_GPL(save_stack_trace_regs); #ifdef CONFIG_HAVE_RELIABLE_STACKTRACE -int -save_stack_trace_tsk_reliable(struct task_struct *tsk, - struct stack_trace *trace) +static int __save_stack_trace_tsk_reliable(struct task_struct *tsk, + struct stack_trace *trace) { unsigned long sp; unsigned long stack_page = (unsigned long)task_stack_page(tsk); @@ -193,6 +197,25 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk, } return 0; } + +int save_stack_trace_tsk_reliable(struct task_struct *tsk, + struct stack_trace *trace) +{ + int ret; + + /* + * If the task doesn't have a stack (e.g., a zombie), the stack is + * "reliably" empty. + */ + if (!try_get_task_stack(tsk)) + return 0; + + ret = __save_stack_trace_tsk_reliable(tsk, trace); + + put_task_stack(tsk); + + return ret; +} EXPORT_SYMBOL_GPL(save_stack_trace_tsk_reliable); #endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */ -- 2.13.3