Messages in this thread | | | Date | Wed, 13 Oct 2021 14:12:36 +0200 | From | Christian Brauner <> | Subject | Re: [PATCH v2 2/2] mm: use pidfd_get_task() |
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On Tue, Oct 12, 2021 at 04:13:31PM +0200, David Hildenbrand wrote: > On 11.10.21 15:32, Christian Brauner wrote: > > From: Christian Brauner <christian.brauner@ubuntu.com> > > > > Instead of duplicating the same code in two places use the newly added > > pidfd_get_task() helper. This fixes an (unimportant for now) bug where > > PIDTYPE_PID is used whereas PIDTYPE_TGID should have been used. > > What would have been the effect of the BUG? Is it worth Fixes: or better
Right now, there's no issue. I hope my "unimportant for now" gets that across. Retrieving it via PIDTYPE_PID or PIDTYPE_TGID doesn't matter right now because at pidfd creation time we ensure that: - the pid used with pidfd_open() - the task created via clone{3}()'s CLONE_PIDFD are used as PIDTYPE_TGID, i.e. the struct pid the pidfd references is used as PIDTYPE_TGID, i.e. is a thread-group leader. The concern is for the future were we may want to enable pidfds to refer to individual threads. Once that happens the passed in pidfd to e.g. process_mrelease() or process_madvise() can refer to a struct pid that is only used as PIDTYPE_PID and not as PIDTYPE_TGID, i.e. it might be a pidfd refering to a non-threadgroup leader. Once that happens we want to make sure that all users of pidfds are ok working with non-threadgroup leaders. If we have on central helper that becomes a relatively simple exercise in grepping and we're sure that all current callers use PIDTYPE_TGID as they're using the helper. If we let places use PIDTYPE_PID or PIDTYPE_TGID interchangeably this becomes a more arduous task. So in a sense it's a bug-in-the-making. It's arguably fixes the addition of process_mrelease() since I mentioned this pretty early on and requested the addition of a helper as part of the patchset. I think it just got lost in the reviews though.
> even separating out the fix? > > > > > Link: https://lore.kernel.org/r/20211004125050.1153693-3-christian.brauner@ubuntu.com > > Cc: Vlastimil Babka <vbabka@suse.cz> > > Cc: Suren Baghdasaryan <surenb@google.com> > > Cc: Matthew Bobrowski <repnop@google.com> > > Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com> > > Cc: David Hildenbrand <david@redhat.com> > > Cc: Jan Kara <jack@suse.cz> > > Cc: Minchan Kim <minchan@kernel.org> > > Reviewed-by: Matthew Bobrowski <repnop@google.com> > > Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> > > --- > > /* v2 */ > > unchanged > > Acked-by: David Hildenbrand <david@redhat.com>
Thanks! Christian
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