| Message ID | 1591947707-15140-1-git-send-email-wangqing@vivo.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: smp call when task currently running on other cpu | expand |
On Fri, Jun 12, 2020 at 03:41:46PM +0800, Wang Qing wrote: > We cannot get FP and PC when the task is running on another CPU, > task->thread.cpu_context is the last time the task was switched out, > we can use smp call to print backtrace itself. > > Signed-off-by: Wang Qing <wangqing@vivo.com> Sorry, but NAK to this as-is. This is not a legitimate use of dump_backtrace(), and even if we wanted to dump a backtrace of a remotely running task, the patch is: * Insufficient, since a remotely running task can become blocked after task_curr() is sampled. * Insufficient and incorrect, since the task can be rescheduled after task->cpu is sampled. This patch could cause *another* task to dump a stacktrace. * Unsafe, since tsk->cpu is accessed racily. In practice we'd likely get away with that, but it's not something we should rely on. * Unsafe, since if this were ever called in IRQ context it could result in a deadlock. Taking a step back, please explain *why* you think you need this? What code in mainline is calling dumop_backtrace() on a remotely running task? Thanks, Mark. > --- > arch/arm64/kernel/traps.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > mode change 100644 => 100755 arch/arm64/kernel/traps.c > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > index 50cc30a..17a07b9 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -83,6 +83,11 @@ static void dump_kernel_instr(const char *lvl, struct pt_regs *regs) > printk("%sCode: %s\n", lvl, str); > } > > +static void dump_backtrace_smp_fun(struct task_struct *tsk) > +{ > + dump_backtrace(NULL, tsk, KERN_DEFAULT); > +} > + > void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, > const char *loglvl) > { > @@ -107,6 +112,12 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, > start_backtrace(&frame, > (unsigned long)__builtin_frame_address(0), > (unsigned long)dump_backtrace); > + } else if (task_curr(tsk)) { > + /* > + * The task is currently running on other cpu > + */ > + smp_call_function_single(tsk->cpu, dump_backtrace_fun, tsk, 0); > + return; > } else { > /* > * task blocked in __switch_to > -- > 2.7.4 >
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index 50cc30a..17a07b9 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -83,6 +83,11 @@ static void dump_kernel_instr(const char *lvl, struct pt_regs *regs) printk("%sCode: %s\n", lvl, str); } +static void dump_backtrace_smp_fun(struct task_struct *tsk) +{ + dump_backtrace(NULL, tsk, KERN_DEFAULT); +} + void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, const char *loglvl) { @@ -107,6 +112,12 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, start_backtrace(&frame, (unsigned long)__builtin_frame_address(0), (unsigned long)dump_backtrace); + } else if (task_curr(tsk)) { + /* + * The task is currently running on other cpu + */ + smp_call_function_single(tsk->cpu, dump_backtrace_fun, tsk, 0); + return; } else { /* * task blocked in __switch_to
We cannot get FP and PC when the task is running on another CPU, task->thread.cpu_context is the last time the task was switched out, we can use smp call to print backtrace itself. Signed-off-by: Wang Qing <wangqing@vivo.com> --- arch/arm64/kernel/traps.c | 11 +++++++++++ 1 file changed, 11 insertions(+) mode change 100644 => 100755 arch/arm64/kernel/traps.c