Re: [syzbot] memory leak in xas_create

From: Matthew Wilcox
Date: Thu Jul 14 2022 - 12:27:44 EST

On Tue, Jul 12, 2022 at 03:29:29PM +0200, Dmitry Vyukov wrote:
> Then I think it's still possible that this is a KMEMLEAK false
> positive. IIRC it may have some false positives since it does not do
> full stop-the-world before scanning memory/registers. syzkaller tries
> to circumvent this by doing multiple scans with some delays, but it
> does not give 100% guarantee.
> And I am assuming this code does not try to hide pointers by storing
> something in low/high bits, etc.

Oh, I meant to answer this. The XArray does set bit 1 of the pointer
when it's stored in the tree. However, this shouldn't affect kmemleak
(I would think) because it looks like a pointer to the third byte of the
allocation, so the allocation is still referenced, even if the first
byte of the allocation isn't referenced.

Also, I would expect kmemleak to report bugs all over if this were the
problem, because every node no matter how it's allocated gets its bit 1