linux-ext4 - Re: [PATCH] Forcing subclasses to have same name pointer as their parent class

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Message-ID: <Zox8ep23zUSzbFMZ@boqun-archlinux>
Date: Mon, 8 Jul 2024 16:55:38 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: ahmed Ehab <bottaawesome633@...il.com>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, linux-ext4@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	syzkaller@...glegroups.com, "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] Forcing subclasses to have same name pointer as their
 parent class

On Tue, Jul 09, 2024 at 02:26:05AM +0300, ahmed Ehab wrote:
> Hi,
>  thanks for the great feedback.
> 
> 
> 
> 
> * Last but not the least, could you try to add a test case in
> lib/locking-selftest.c to ensure the issue you fixed won't        happen
> again? This could be tricky, since you will need to fight        against
> the compiler to generate two string literals with the        same content.*
> I added a test case, but I am not sure how to run this test file as it
> doesn't seem to be part of the kselftests. I compiled it successfully by
> setting the lock debugging option but couldn't get it to run.
> 

My usual approach is: set CONFIG_DEBUG_LOCKING_API_SELFTESTS=y, compile
a kernel, and boot it in qemu, the test result will show in serial log
of the VM. Hope that helps.

Regards,
Boqun

> Regards,
> Ahmed
> 
> On Thu, Jul 4, 2024 at 1:46 AM Boqun Feng <boqun.feng@...il.com> wrote:
> 
> > Hi,
> >
> > On Thu, Jul 04, 2024 at 03:32:24AM +0300, botta633 wrote:
> > > Preventing Lockdep_set_subclass from creating a new instance of the
> > > string literal. Hence, we will always have the class->name. This
> > > prevents kernel panics when locking up a lock class while comparing
> > > class locks and class names.
> >
> > Good catch! Thanks.
> >
> > >
> > >
> >
> > Please remove the extra blank line here.
> >
> > > Signed-off-by: botta633 <bottaawesome633@...il.com>
> >
> > Do you mind putting your real name here? Besides, IIUC, this is fixing:
> >
> >         https://syzkaller.appspot.com/bug?extid=7f4a6f7f7051474e40ad
> >
> >
> > , right? If so, there are some more things:
> >
> > *       Copy ext4 and syzkaller people, so that you could get more
> >         tests.
> >
> > *       Since this is a bug fix, could you please figure out which
> >         commit introduces the issue, so that you can put a correct
> >         "Fixes:" tag along with your signed-off-by?
> >
> > *       Since the issue was reported by syzkaller, you should put their
> >         "Reported-by" tag, they have an example in the website I paste
> >         above.
> >
> > *       Please also Cc stable mail list so that the fix can be
> >         backported, you can find the information on "Cc: stable" tag at:
> >
> >                 https://docs.kernel.org/process/stable-kernel-rules.html
> >
> > *       Last but not the least, could you try to add a test case in
> >         lib/locking-selftest.c to ensure the issue you fixed won't
> >         happen again? This could be tricky, since you will need to fight
> >         against the compiler to generate two string literals with the
> >         same content.
> >
> > [Cc ext4 and syzkaller]
> >
> > Regards,
> > Boqun
> >
> > > ---
> > >  include/linux/lockdep.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> > > index 08b0d1d9d78b..df8fa5929de7 100644
> > > --- a/include/linux/lockdep.h
> > > +++ b/include/linux/lockdep.h
> > > @@ -173,7 +173,7 @@ static inline void lockdep_init_map(struct
> > lockdep_map *lock, const char *name,
> > >                             (lock)->dep_map.lock_type)
> > >
> > >  #define lockdep_set_subclass(lock, sub)
> >       \
> > > -     lockdep_init_map_type(&(lock)->dep_map, #lock,
> > (lock)->dep_map.key, sub,\
> > > +     lockdep_init_map_type(&(lock)->dep_map, (lock)->dep_map.name,
> > (lock)->dep_map.key, sub,\
> > >                             (lock)->dep_map.wait_type_inner,          \
> > >                             (lock)->dep_map.wait_type_outer,          \
> > >                             (lock)->dep_map.lock_type)
> > > --
> > > 2.45.2
> > >
> >