linux-kernel - Re: [PATCH] 9p: Avoid creating multiple slab caches with the same name

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Message-ID: <ZxafcO8KWMlXaeWE@telecaster.dhcp.thefacebook.com>
Date: Mon, 21 Oct 2024 11:37:36 -0700
From: Omar Sandoval <osandov@...ndov.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Dominique Martinet <asmadeus@...ewreck.org>,
	Thorsten Leemhuis <regressions@...mhuis.info>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Eric Van Hensbergen <ericvh@...nel.org>,
	Christian Schoenebeck <linux_oss@...debyte.com>,
	v9fs@...ts.linux.dev, linux-kernel@...r.kernel.org,
	regressions@...ts.linux.dev, Jason Gunthorpe <jgg@...dia.com>,
	Pedro Falcato <pedro.falcato@...il.com>
Subject: Re: [PATCH] 9p: Avoid creating multiple slab caches with the same
 name

On Mon, Oct 21, 2024 at 10:42:02AM +0200, Vlastimil Babka wrote:
> On 10/19/24 02:02, Dominique Martinet wrote:
> > Vlastimil Babka wrote on Fri, Oct 18, 2024 at 11:38:04PM +0200:
> >> > In that case: Linus, given the circumstances I wonder if it would be
> >> > best if you could merge the patch at the start of this thread
> >> > (https://lore.kernel.org/all/20240807094725.2193423-1-pedro.falcato@gmail.com/
> >> > ) directly, which can also be found as 79efebae4afc22 in -next if you
> >> > prefer to cherry-pick it from there  Either now or after 24 to 36 hours,
> >> > which would give Eric a chance to ACK/NACK this if he sees this mail.
> > 
> > Sorry to everyone involved, I've just sent the merge request - I wasn't
> > much at computer in the past few weeks so wanted to wait until I got
> > back home to send it just in case, as I didn't realize this was a recent
> > regression that caused actual harm (it sounded like an old warning that
> > someone just recently happened to hit, and sounded easy enough to work
> > around locally if there is only one specific setup involved); I should
> > have sent the fix separately or at least corrected myself about the
> > schedule.
> > 
> >> >>> It is causing regressions in my environment
> >> >>> #regzbot introduced: 4c39529663b9
> >> > 
> >> > If anyone wonders, that is 4c39529663b931 ("slab: Warn on duplicate
> >> > cache names when DEBUG_VM=y") [v6.12-rc1]. That's also why I'm CCing
> >> > Vlastimil, so he knows about this.
> > 
> > (that might have been nice to have as a Fixes tag for eventual backport,
> > but at least that commit doesn't appear to have been picked up by stable
> > so it's probably fine as is)
> 
> Yeah it's missing the tag because I believe Pedro sent the 9p fix before
> sending the new warning patch itself, so there was even no commit ID yet.
> The plan was to introduce the warning only after all pre-existing in-tree
> code that would triggers it was fixed. I just assumed the fix would be
> mainlined before/at the same time as the warning itself, but forgot to
> check. In any case if I see e.g. autosel picking the warning patch for
> stable, I'll object.
> 
> Thanks,
> Vlastimil

FYI, drgn's CI started getting EIO errors from
getdents("/sys/kernel/slab") that I bisected to this patch. The problem
is that dev_name can be an arbitrary string. In my case, it is
"/dev/root". This trips verify_dirent_name(), which fails if a filename
contains a slash.

This needs to use a different unique identifier. Maybe clnt->msize? But
then the kmem_caches will need to be shared between different mounts
using the same msize.

In any case, can this be reverted for now?

Thanks,
Omar