From: Chuck Lever III <chuck.lever@xxxxxxxxxx>
Date: Sat, 16 Jul 2022 16:18:41 +0000
> > On Jul 15, 2022, at 9:31 PM, Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> wrote:
> >
> > Two functions, flock syscall and locks_remove_flock(), call
> > flock_make_lock(). It allocates struct file_lock from slab
> > cache if its argument fl is NULL.
> >
> > When we call flock syscall, we pass NULL to allocate memory
> > for struct file_lock. However, we always free it at the end
> > by locks_free_lock(). We need not allocate it and instead
> > should use a local variable as locks_remove_flock() does.
> >
> > Also, the validation for flock_translate_cmd() is not necessary
> > for locks_remove_flock(). So we move the part to flock syscall
> > and make flock_make_lock() return nothing.
> >
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
>
> It looks like a reasonable clean-up. Handful of comments below.
>
> Reviewed-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Thank you for reviewing!
> > ---
> > fs/locks.c | 57 +++++++++++++++++++-----------------------------------
> > 1 file changed, 20 insertions(+), 37 deletions(-)
> >
> > diff --git a/fs/locks.c b/fs/locks.c
> > index ca28e0e50e56..db75f4537abc 100644
> > --- a/fs/locks.c
> > +++ b/fs/locks.c
> > @@ -425,21 +425,9 @@ static inline int flock_translate_cmd(int cmd) {
> > }
> >
> > /* Fill in a file_lock structure with an appropriate FLOCK lock. */
> > -static struct file_lock *
> > -flock_make_lock(struct file *filp, unsigned int cmd, struct file_lock *fl)
> > +static void flock_make_lock(struct file *filp, struct file_lock *fl, int type)
> > {
> > - int type = flock_translate_cmd(cmd);
> > -
> > - if (type < 0)
> > - return ERR_PTR(type);
> > -
> > - if (fl == NULL) {
> > - fl = locks_alloc_lock();
> > - if (fl == NULL)
> > - return ERR_PTR(-ENOMEM);
> > - } else {
> > - locks_init_lock(fl);
> > - }
> > + locks_init_lock(fl);
> >
> > fl->fl_file = filp;
> > fl->fl_owner = filp;
> > @@ -447,8 +435,6 @@ flock_make_lock(struct file *filp, unsigned int cmd, struct file_lock *fl)
> > fl->fl_flags = FL_FLOCK;
> > fl->fl_type = type;
> > fl->fl_end = OFFSET_MAX;
> > -
> > - return fl;
> > }
> >
> > static int assign_type(struct file_lock *fl, long type)
> > @@ -2097,14 +2083,18 @@ EXPORT_SYMBOL(locks_lock_inode_wait);
> > */
> > SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
> > {
> > - struct fd f = fdget(fd);
> > - struct file_lock *lock;
> > - int can_sleep, unlock;
> > + int can_sleep, unlock, type;
> > + struct file_lock fl;
> > + struct fd f;
> > int error;
>
> "struct file_lock" on my system is 216 bytes. That's a lot to
> allocate on the stack, but there isn't much else there in
> addition to "struct file_lock", so OK.
>
>
> > - error = -EBADF;
> > + type = flock_translate_cmd(cmd);
> > + if (type < 0)
> > + return type;
> > +
> > + f = fdget(fd);
> > if (!f.file)
> > - goto out;
> > + return -EBADF;
> >
> > can_sleep = !(cmd & LOCK_NB);
> > cmd &= ~LOCK_NB;
> > @@ -2127,32 +2117,25 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
> > goto out_putf;
> > }
> >
> > - lock = flock_make_lock(f.file, cmd, NULL);
> > - if (IS_ERR(lock)) {
> > - error = PTR_ERR(lock);
> > - goto out_putf;
> > - }
> > + flock_make_lock(f.file, &fl, type);
> >
> > if (can_sleep)
> > - lock->fl_flags |= FL_SLEEP;
> > + fl.fl_flags |= FL_SLEEP;
> >
> > - error = security_file_lock(f.file, lock->fl_type);
> > + error = security_file_lock(f.file, fl.fl_type);
> > if (error)
> > - goto out_free;
> > + goto out_putf;
> >
> > if (f.file->f_op->flock)
> > error = f.file->f_op->flock(f.file,
> > - (can_sleep) ? F_SETLKW : F_SETLK,
> > - lock);
> > + can_sleep ? F_SETLKW : F_SETLK,
> > + &fl);
> > else
> > - error = locks_lock_file_wait(f.file, lock);
> > -
> > - out_free:
> > - locks_free_lock(lock);
> > + error = locks_lock_file_wait(f.file, &fl);
> >
> > out_putf:
> > fdput(f);
> > - out:
> > +
> > return error;
> > }
> >
> > @@ -2614,7 +2597,7 @@ locks_remove_flock(struct file *filp, struct file_lock_context *flctx)
> > if (list_empty(&flctx->flc_flock))
> > return;
> >
> > - flock_make_lock(filp, LOCK_UN, &fl);
> > + flock_make_lock(filp, &fl, flock_translate_cmd(LOCK_UN));
>
> We hope the compiler recognizes that passing a constant value through
> a switch statement means the flock_translate_cmd() call here is
> reduced to a constant F_UNLCK. It might be slightly easier to read
> if you explicitly pass F_UNLCK here? Dunno.
My thoughts exactly. I wrote this way because flock_translate_cmd() was
called in flock_make_lock(), so I guessed there might be coding conventions
like we should try to use uAPI value.
I have no strong preference though, if there is no such convention, I like
using F_UNLCK directly instead of trusting the compiler.
> > fl.fl_flags |= FL_CLOSE;
> >
> > if (filp->f_op->flock)
> > --
> > 2.30.2
> >
>
> --
> Chuck Lever
