On Mon 24-10-16 17:25:03, Arnd Bergmann wrote:
> After enabling -Wmaybe-uninitialized warnings, we get a false-postive
> warning for shmem:
>
> mm/shmem.c: In function ‘shmem_getpage_gfp’:
> include/linux/spinlock.h:332:21: error: ‘info’ may be used uninitialized in
> this function [-Werror=maybe-uninitialized]
Is this really a false positive? If we goto clear and then
if (sgp <= SGP_CACHE &&
((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
if (alloced) {
we could really take a spinlock on an unitialized variable. But maybe
there is something that prevents from that... Anyway the whole
shmem_getpage_gfp is really hard to follow due to gotos and labels
proliferation.
> This can be easily avoided, since the correct 'info' pointer is known
> at the time we first enter the function, so we can simply move the
> initialization up. Moving it before the first label avoids the
> warning.
>
> Signed-off-by: Arnd Bergmann <[email protected]>
Looks good to me.
Acked-by: Michal Hocko <[email protected]>
> ---
> mm/shmem.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index ad7813d73ea7..69e6777096a3 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1537,7 +1537,7 @@ static int shmem_getpage_gfp(struct inode *inode,
> pgoff_t index,
> struct mm_struct *fault_mm, int *fault_type)
> {
> struct address_space *mapping = inode->i_mapping;
> - struct shmem_inode_info *info;
> + struct shmem_inode_info *info = SHMEM_I(inode);
> struct shmem_sb_info *sbinfo;
> struct mm_struct *charge_mm;
> struct mem_cgroup *memcg;
> @@ -1587,7 +1587,6 @@ static int shmem_getpage_gfp(struct inode *inode,
> pgoff_t index,
> * Fast cache lookup did not find it:
> * bring it back from swap or allocate.
> */
> - info = SHMEM_I(inode);
> sbinfo = SHMEM_SB(inode->i_sb);
> charge_mm = fault_mm ? : current->mm;
>
> --
> 2.9.0
>
--
Michal Hocko
SUSE Labs
