Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 5 Jan 2022 11:13:30 -0800 | Subject | Re: psi_trigger_poll() is completely broken |
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On Wed, Jan 5, 2022 at 11:07 AM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > Whoever came up with that stupid "replace existing trigger with a > write()" model should feel bad. It's garbage, and it's actively buggy > in multiple ways.
What are the users? Can we make the rule for -EBUSY simply be that you can _install_ a trigger, but you can't replace an existing one (except with NULL, when you close it).
That would fix the poll() lifetime issue, and would make the psi_trigger_replace() races fairly easy to fix - just use
if (cmpxchg(trigger_ptr, NULL, new) != NULL) { ... free 'new', return -EBUSY ..
to install the new one, instead of
rcu_assign_pointer(*trigger_ptr, new);
or something like that. No locking necessary.
But I assume people actually end up re-writing triggers, because people are perverse and have taken advantage of this completely broken API.
Linus
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