Re: [PATCH v2 02/12] uprobes: correct mmap_sem locking assumptions in uprobe_write_opcode()

Andrii Nakryiko
2024-07-03T18:25:48Z

On Wed, Jul 3, 2024 at 6:15 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Mon, 1 Jul 2024 15:39:25 -0700
> Andrii Nakryiko <andrii@kernel.org> wrote:
>
> > It seems like uprobe_write_opcode() doesn't require writer locked
> > mmap_sem, any lock (reader or writer) should be sufficient. This was
> > established in a discussion in [0] and looking through existing code
> > seems to confirm that there is no need for write-locked mmap_sem.
> >
> > Fix the comment to state this clearly.
> >
> > [0] https://lore.kernel.org/linux-trace-kernel/20240625190748.GC14254@redhat.com/
> >
> > Fixes: 29dedee0e693 ("uprobes: Add mem_cgroup_charge_anon() into uprobe_write_opcode()")
>
> nit: why this has Fixes but [01/12] doesn't?
>
> Should I pick both to fixes branch?

I'd keep both of them in probes/for-next, tbh. They are not literally
fixing anything, just cleaning up comments. I can drop the Fixes tag
from this one, if you'd like.

>
> Thank you,
>
> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> > ---
> > kernel/events/uprobes.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index 081821fd529a..f87049c08ee9 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -453,7 +453,7 @@ static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
> > * @vaddr: the virtual address to store the opcode.
> > * @opcode: opcode to be written at @vaddr.
> > *
> > - * Called with mm->mmap_lock held for write.
> > + * Called with mm->mmap_lock held for read or write.
> > * Return 0 (success) or a negative errno.
> > */
> > int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> > --
> > 2.43.0
> >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>