Re: [PATCH] fs: use debug-only asserts around fd allocation and install

[Christian Brauner <brauner@kernel.org>]

On Wed, Mar 12, 2025 at 06:21:01PM +0100, Mateusz Guzik wrote:
> On Wed, Mar 12, 2025 at 5:19 PM Mateusz Guzik <mjguzik@gmail.com> wrote:
> >
> > This also restores the check which got removed in 52732bb9abc9ee5b
> > ("fs/file.c: remove sanity_check and add likely/unlikely in alloc_fd()")
> > for performance reasons -- they no longer apply with a debug-only
> > variant.
> >
> > Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
> > ---
> >
> > I have about 0 opinion whether this should be BUG or WARN, the code was
> > already inconsistent on this front. If you want the latter, I'll have 0
> > complaints if you just sed it and commit as yours.
> >
> > This reminded me to sort out that litmus test for smp_rmb, hopefully
> > soon(tm) as it is now nagging me.
> >
> >  fs/file.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/file.c b/fs/file.c
> > index 6c159ede55f1..09460ec74ef8 100644
> > --- a/fs/file.c
> > +++ b/fs/file.c
> > @@ -582,6 +582,7 @@ static int alloc_fd(unsigned start, unsigned end, unsigned flags)
> >
> >         __set_open_fd(fd, fdt, flags & O_CLOEXEC);
> >         error = fd;
> > +       VFS_BUG_ON(rcu_access_pointer(fdt->fd[fd]) != NULL);
> >
> 
> when restoring this check i dutifully copy-pasted the original. I only
> now mentally registered it uses a rcu primitive to do the load, while
> the others do a plain load. arguably the former is closer to being
> correct and it definitely does not hurt
> 
> so this line should replace the other 2 lines below. i can send a v2
> to that effect, but given the triviality of the edit, perhaps you will
> be happy to sort it out

Yes, sure. Done!