On Tue, Dec 19, 2017 at 08:58:23AM -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>
> The __cond_lock macro expects the function to return 'true' if the lock
> was acquired and 'false' if it wasn't. We have another common calling
> convention in the kernel, which is returning 0 on success and an errno
> on failure. It's hard to use the existing __cond_lock macro for those
> kinds of functions, so introduce __cond_lock_err() and convert the
> two existing users.
This is much cleaner! One quick issue below.
> Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
> ---
> include/linux/compiler_types.h | 2 ++
> include/linux/mm.h | 9 ++-------
> mm/memory.c | 9 ++-------
> 3 files changed, 6 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 6b79a9bba9a7..ff3c41c78efa 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -16,6 +16,7 @@
> # define __acquire(x) __context__(x,1)
> # define __release(x) __context__(x,-1)
> # define __cond_lock(x,c) ((c) ? ({ __acquire(x); 1; }) : 0)
> +# define __cond_lock_err(x,c) ((c) ? 1 : ({ __acquire(x); 0; }))
^
I think we actually want this to return c here ^
The old code saved off the actual return value from __follow_pte_pmd() (say,
-EINVAL) in 'res', and that was what was returned on error from both
follow_pte_pmd() and follow_pte(). The value of 1 returned by __cond_lock()
was just discarded (after we cast it to void for some reason).
With this new code we actually return the value from __cond_lock_err(), which
means that instead of returning -EINVAL, we'll return 1 on error.
> # define __percpu __attribute__((noderef, address_space(3)))
> # define __rcu __attribute__((noderef, address_space(4)))
> # define __private __attribute__((noderef))
> @@ -42,6 +43,7 @@ extern void __chk_io_ptr(const volatile void __iomem *);
> # define __acquire(x) (void)0
> # define __release(x) (void)0
> # define __cond_lock(x,c) (c)
> +# define __cond_lock_err(x,c) (c)
> # define __percpu
> # define __rcu
> # define __private
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 94a9d2149bd6..2ccdc980296b 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1328,13 +1328,8 @@ static inline int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
> unsigned long *start, unsigned long *end,
> pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
> {
> - int res;
> -
> - /* (void) is needed to make gcc happy */
> - (void) __cond_lock(*ptlp,
> - !(res = __follow_pte_pmd(mm, address, start, end,
> - ptepp, pmdpp, ptlp)));
> - return res;
> + return __cond_lock_err(*ptlp, __follow_pte_pmd(mm, address, start, end,
> + ptepp, pmdpp, ptlp));
> }
>
> static inline void unmap_shared_mapping_range(struct address_space *mapping,
> diff --git a/mm/memory.c b/mm/memory.c
> index cb433662af21..92d58309cf45 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4269,13 +4269,8 @@ int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
> static inline int follow_pte(struct mm_struct *mm, unsigned long address,
> pte_t **ptepp, spinlock_t **ptlp)
> {
> - int res;
> -
> - /* (void) is needed to make gcc happy */
> - (void) __cond_lock(*ptlp,
> - !(res = __follow_pte_pmd(mm, address, NULL, NULL,
> - ptepp, NULL, ptlp)));
> - return res;
> + return __cond_lock_err(*ptlp, __follow_pte_pmd(mm, address, NULL, NULL,
> + ptepp, NULL, ptlp));
> }
>
> /**
> --
> 2.15.1
>
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