Re: [PATCH] mm/userfaultfd: prevent busy looping for tasks with signals pending

[Peter Xu <peterx@redhat.com>]

On Fri, Apr 25, 2025 at 05:52:20AM +0100, Matthew Wilcox wrote:
> Because "interruptible" means it can be interrupted by inane stuff like
> SIGWINCH and SIGALRM.  And then we return from a page fault prematurely
> and can't actually handle the situation, so we end up going back into the
> page fault handler anyway having accomplished nothing other than burn CPU.
> 
> At least it's better than interruptible system calls which just gets
> you short reads, corrupted data and crashing programs.

I see where it came from now, thanks.

IIUC it'll be a major spinning issue only if the fault is generated from
the sighandler itself which spins on its own. The hope is that sighandler
should almost always be suggested to be as tiny as possible, to make it
unlikely to happen.  Said that, it's a valid point indeed.

Maybe we should make FAULT_FLAG_INTERRUPTIBLE a hint rather than a request
to handle_mm_fault(), so the internal of page resolution can decide whether
to respect the hint.

Thanks,

-- 
Peter Xu