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powerpc: prep stack walkers for THREAD_INFO_IN_TASK

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[text copied from commit 9bbd4c56b0
("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.rutland@arm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Move try_get_task_stack() below tsk == NULL check in show_stack()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Christophe Leroy 2019-01-31 10:08:52 +00:00 • committed by Michael Ellerman
parent 054860897c
commit 018cce33c5
2 changed files with 49 additions and 6 deletions
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29
arch/powerpc/kernel/stacktrace.c
View file

@ -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);
@ -90,9 +95,8 @@ EXPORT_SYMBOL_GPL(save_stack_trace_regs);
*
* If the task is not 'current', the caller *must* ensure the task is inactive.
*/
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 newsp;
@ -197,6 +201,25 @@ 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 */