Re: [PATCH v3] mm: Fix possible deadlock in console_trylock_spinning

[Catalin Marinas <catalin.marinas@arm.com>]

On Thu, Aug 14, 2025 at 04:54:33PM +0200, Greg Kroah-Hartman wrote:
> On Thu, Aug 14, 2025 at 03:38:23PM +0100, Catalin Marinas wrote:
> > On Thu, Aug 14, 2025 at 03:56:58PM +0200, Greg Kroah-Hartman wrote:
> > > On Thu, Aug 14, 2025 at 02:08:35PM +0100, Catalin Marinas wrote:
> > > > On Thu, Aug 14, 2025 at 10:33:56AM +0800, Gu Bowen wrote:
> > > > > On 8/14/2025 6:56 AM, Andrew Morton wrote:
> > > > > > I'm not sure which kernel version this was against, but kmemleak.c has
> > > > > > changed quite a lot.
> > > > > > 
> > > > > > Could we please see a patch against a latest kernel version?  Linus
> > > > > > mainline will suit.
> > > > > > 
> > > > > > Thanks.
> > > > > 
> > > > > I discovered this issue in kernel version 5.10. Afterwards, I reviewed the
> > > > > code of the mainline version and found that this deadlock path no longer
> > > > > exists due to the refactoring of console_lock in v6.2-rc1. For details on
> > > > > the refactoring, you can refer to this link :
> > > > > https://lore.kernel.org/all/20221116162152.193147-1-john.ogness@linutronix.de/.
> > > > > Therefore, theoretically, this issue existed before the refactoring of
> > > > > console_lock.
> > > > 
> > > > Oh, so you can no longer hit this issue with mainline. This wasn't
> > > > mentioned (or I missed it) in the commit log.
> > > > 
> > > > So this would be a stable-only fix that does not have a correspondent
> > > > upstream. Adding Greg for his opinion.
> > > 
> > > Why not take the upstream changes instead?
> > 
> > Gu reckons there are 40 patches -
> > https://lore.kernel.org/all/20221116162152.193147-1-john.ogness@linutronix.de/
> 
> 40 really isn't that much overall, we've taken way more for much smaller
> issues :)

TBH, I'm not sure it's worth it. That's a potential deadlock on a rare
error condition (a kmemleak bug or something wrong with the sites
calling the kmemleak API).

> > I haven't checked what ended in mainline and whether we could do with
> > fewer backports.
> 
> I'll leave that all up to the people who are still wanting these older
> kernels.

Good point. Thanks for the advice ;).

-- 
Catalin