linux-kernel - Re: [RFC PATCH] vfs: add inode lockdep assertions

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZPiaYjcTMyuM0JL5@casper.infradead.org>
Date:   Wed, 6 Sep 2023 16:27:30 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Bernd Schubert <bernd.schubert@...tmail.fm>
Cc:     Mateusz Guzik <mjguzik@...il.com>, brauner@...nel.org,
        viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH] vfs: add inode lockdep assertions

On Wed, Sep 06, 2023 at 05:23:42PM +0200, Bernd Schubert wrote:
> 
> 
> On 9/6/23 17:20, Matthew Wilcox wrote:
> > On Thu, Aug 31, 2023 at 05:14:14PM +0200, Mateusz Guzik wrote:
> > > +++ b/include/linux/fs.h
> > > @@ -842,6 +842,16 @@ static inline void inode_lock_shared_nested(struct inode *inode, unsigned subcla
> > >   	down_read_nested(&inode->i_rwsem, subclass);
> > >   }
> > > +static inline void inode_assert_locked(struct inode *inode)
> > > +{
> > > +	lockdep_assert_held(&inode->i_rwsem);
> > > +}
> > > +
> > > +static inline void inode_assert_write_locked(struct inode *inode)
> > > +{
> > > +	lockdep_assert_held_write(&inode->i_rwsem);
> > > +}
> > 
> > This mirrors what we have in mm, but it's only going to trigger on
> > builds that have lockdep enabled.  Lockdep is very expensive; it
> > easily doubles the time it takes to run xfstests on my laptop, so
> > I don't generally enable it.  So what we also have in MM is:
> > 
> > static inline void mmap_assert_write_locked(struct mm_struct *mm)
> > {
> >          lockdep_assert_held_write(&mm->mmap_lock);
> >          VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
> > }
> > 
> > Now if you have lockdep enabled, you get the lockdep check which
> > gives you all the lovely lockdep information, but if you don't, you
> > at least get the cheap check that someone is holding the lock at all.
> > 
> > ie I would make this:
> > 
> > +static inline void inode_assert_write_locked(struct inode *inode)
> > +{
> > +	lockdep_assert_held_write(&inode->i_rwsem);
> > +	WARN_ON_ONCE(!inode_is_locked(inode));
> > +}
> > 
> > Maybe the locking people could give us a rwsem_is_write_locked()
> > predicate, but until then, this is the best solution we came up with.
> 
> 
> Which is exactly what I had suggested in the other thread :)

Yes, but apparently comments in that thread don't count :eyeroll: