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

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Wed, 3 Jul 2024 11:25:35 -0700
Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:

> 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.

Got it. Usually cleanup patch will not have Fixed tag, so if you don't mind,
please drop it.

Thank you,

> 
> >
> > 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>


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>