Messages in this thread | | | Date | Mon, 20 Apr 2020 15:24:28 -0700 | From | Sami Tolvanen <> | Subject | Re: [PATCH v11 03/12] scs: add support for stack usage debugging |
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On Mon, Apr 20, 2020 at 06:17:42PM +0100, Will Deacon wrote: > > +#ifdef CONFIG_DEBUG_STACK_USAGE > > +static inline unsigned long scs_used(struct task_struct *tsk) > > +{ > > + unsigned long *p = __scs_base(tsk); > > + unsigned long *end = scs_magic(p); > > + unsigned long s = (unsigned long)p; > > + > > + while (p < end && READ_ONCE_NOCHECK(*p)) > > + p++; > > I think the expectation is that the caller has already checked that the > stack is not corrupted, so I'd probably throw a couple of underscores > in front of the function name, along with a comment.
Correct. I'll do that.
> Also, is tsk ever != current?
This is only called from scs_release(), so tsk is never current.
> > +static void scs_check_usage(struct task_struct *tsk) > > +{ > > + static DEFINE_SPINLOCK(lock); > > + static unsigned long highest; > > + unsigned long used = scs_used(tsk); > > + > > + if (used <= highest) > > + return; > > + > > + spin_lock(&lock); > > + > > + if (used > highest) { > > + pr_info("%s (%d): highest shadow stack usage: %lu bytes\n", > > + tsk->comm, task_pid_nr(tsk), used); > > + highest = used; > > + } > > + > > + spin_unlock(&lock); > > Do you really need this lock? I'd have thought you could cmpxchg() > highest instead.
This is similar to check_stack_usage in kernel/exit.c, but yes, I can change this to a cmpxchg() loop instead.
Sami
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