linux-kernel - Re: [PATCH v2 5/5] fs: Add inode_assert_locked() and inode_assert_locked

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Message-ID: <ZSMZkuJGgHyyqDWP@casper.infradead.org>
Date:   Sun, 8 Oct 2023 22:05:22 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Mateusz Guzik <mjguzik@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Chandan Babu R <chandan.babu@...cle.com>,
        "Darrick J . Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v2 5/5] fs: Add inode_assert_locked() and
 inode_assert_locked_excl()

On Sun, Oct 08, 2023 at 10:26:40PM +0200, Mateusz Guzik wrote:
> On 10/7/23, Matthew Wilcox (Oracle) <willy@...radead.org> wrote:
> > +static inline void inode_assert_locked_excl(const struct inode *inode)
> > +{
> > +	rwsem_assert_held_write(&inode->i_rwsem);
> > +}
> > +
> >  static inline void inode_lock_nested(struct inode *inode, unsigned
> > subclass)
> >  {
> >  	down_write_nested(&inode->i_rwsem, subclass);
> 
> Why "excl" instead of "write"? Apart from looking weird, it is
> inconsistent with "prior art" in the file: i_mmap_assert_write_locked.

Yes, but that pairs with i_mmap_lock_write() / i_mmap_lock_read().

The problem is that we have inode_lock() / inode_lock_shared()
inode_assert_locked_read/write doesn't make sense with them.  But
inode_assert_locked() doesn't make sense as the assertion for
inode_lock() because you'd expect it to assert whether the inode lock
is held at all.  So I went with inode_assert_locked_excl().

I wouldn't mind if we converted all the inode_lock()/shared to
inode_lock_read() / inode_lock_write(), and then added
inode_assert_read_locked() / inode_assert_write_locked().  That's
a bit of a bigger job than I want to take on today.