Re: [PATCH v2 tip/perf/core 5/5] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution

On 10/02, Andrii Nakryiko wrote:

On Wed, Oct 2, 2024 at 12:25 AM Oleg Nesterov [off-list ref] wrote:

quoted

quoted

+     vm_file = READ_ONCE(vma->vm_file);
+     if (!vm_file)
+             return NULL;
+
+     offset = (loff_t)(vma->vm_pgoff << PAGE_SHIFT) + (bp_vaddr - vma->vm_start);

LGTM. But perhaps vma->vm_pgoff and vma->vm_start need READ_ONCE() as well,
if nothing else to shut up KCSAN if this code races with, say, __split_vma() ?

We keep going back and forth between reading directly, using
READ_ONCE(), and annotating with data_race(). I don't think it matters
in terms of correctness or performance, so I'm happy to add whatever
incantations that will make everyone satisfied. Let's see what others
think, and I'll incorporate that into the next revision.

OK, agreed...

And I guess I was wrong anyway, READ_ONCE() alone won't shutup KCSAN in
this case.

Oleg.