From: Christian Brauner <brauner@kernel.org>
To: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Cc: amir73il@gmail.com, hu1.chen@intel.com, miklos@szeredi.hu,
malini.bhandaru@intel.com, tim.c.chen@intel.com,
mikko.ylinen@intel.com, lizhen.you@intel.com,
linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 0/3] overlayfs: Optimize override/revert creds
Date: Thu, 25 Apr 2024 11:20:04 +0200 [thread overview]
Message-ID: <20240425-nullnummer-pastinaken-c8cf2f7c41f3@brauner> (raw)
In-Reply-To: <87a5liy3le.fsf@intel.com>
On Wed, Apr 24, 2024 at 12:15:25PM -0700, Vinicius Costa Gomes wrote:
> Christian Brauner <brauner@kernel.org> writes:
>
> > On Tue, Apr 02, 2024 at 07:18:05PM -0700, Vinicius Costa Gomes wrote:
> >> Hi,
> >>
> >> Changes from RFC v3:
> >> - Removed the warning "fixes" patches, as they could hide potencial
> >> bugs (Christian Brauner);
> >> - Added "cred-specific" macros (Christian Brauner), from my side,
> >> added a few '_' to the guards to signify that the newly introduced
> >> helper macros are preferred.
> >> - Changed a few guard() to scoped_guard() to fix the clang (17.0.6)
> >> compilation error about 'goto' bypassing variable initialization;
> >>
> >> Link to RFC v3:
> >>
> >> https://lore.kernel.org/r/20240216051640.197378-1-vinicius.gomes@intel.com/
> >>
> >> Changes from RFC v2:
> >> - Added separate patches for the warnings for the discarded const
> >> when using the cleanup macros: one for DEFINE_GUARD() and one for
> >> DEFINE_LOCK_GUARD_1() (I am uncertain if it's better to squash them
> >> together);
> >> - Reordered the series so the backing file patch is the first user of
> >> the introduced helpers (Amir Goldstein);
> >> - Change the definition of the cleanup "class" from a GUARD to a
> >> LOCK_GUARD_1, which defines an implicit container, that allows us
> >> to remove some variable declarations to store the overriden
> >> credentials (Amir Goldstein);
> >> - Replaced most of the uses of scoped_guard() with guard(), to reduce
> >> the code churn, the remaining ones I wasn't sure if I was changing
> >> the behavior: either they were nested (overrides "inside"
> >> overrides) or something calls current_cred() (Amir Goldstein).
> >>
> >> New questions:
> >> - The backing file callbacks are now called with the "light"
> >> overriden credentials, so they are kind of restricted in what they
> >> can do with their credentials, is this acceptable in general?
> >
> > Until we grow additional users, I think yes. Just needs to be
> > documented.
> >
>
> Will add some documentation for it, then.
>
> >> - in ovl_rename() I had to manually call the "light" the overrides,
> >> both using the guard() macro or using the non-light version causes
> >> the workload to crash the kernel. I still have to investigate why
> >> this is happening. Hints are appreciated.
> >
> > Do you have a reproducer? Do you have a splat from dmesg?
>
> Just to be sure, with this version of the series the crash doesn't
> happen. It was only happening when I was using the guard() macro
> everywhere.
>
> I just looked at my crash collection and couldn't find the splats, from
> what I remember I lost connection to the machine, and wasn't able to
> retrieve the splat.
>
> I believe the crash and clang 17 compilation error point to the same
> problem, that in ovl_rename() some 'goto' skips the declaration of the
> (implicit) variable that the guard() macro generates. And it ends up
> doing a revert_creds_light() on garbage memory when ovl_rename()
> returns.
If this is a compiler bug this warrants at least a comment in the commit
message because right now people will be wondering why that place
doesn't use a guard. Ideally we can just use guards everywhere though
and report this as a bug against clang, I think.
>
> (if you want I can try and go back to "guard() everywhere" and try a bit
> harder to get a splat)
>
> Does that make sense?
Yes.
next prev parent reply other threads:[~2024-04-25 9:20 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-03 2:18 [PATCH v1 0/3] overlayfs: Optimize override/revert creds Vinicius Costa Gomes
2024-04-03 2:18 ` [PATCH v1 1/3] cred: Add a light version of override/revert_creds() Vinicius Costa Gomes
2024-04-03 2:18 ` [PATCH v1 2/3] fs: Optimize credentials reference count for backing file ops Vinicius Costa Gomes
2024-04-03 15:40 ` kernel test robot
2024-04-03 2:18 ` [PATCH v1 3/3] overlayfs: Optimize credentials usage Vinicius Costa Gomes
2024-04-12 12:36 ` [PATCH v1 0/3] overlayfs: Optimize override/revert creds Miklos Szeredi
2024-04-24 19:01 ` Vinicius Costa Gomes
2024-04-25 6:06 ` Amir Goldstein
2024-04-24 17:01 ` Christian Brauner
2024-04-24 19:15 ` Vinicius Costa Gomes
2024-04-25 9:20 ` Christian Brauner [this message]
2024-04-25 17:12 ` Vinicius Costa Gomes
2024-04-25 17:47 ` Nathan Chancellor
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