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SubjectRe: [PATCH v2] shmem: avoid maybe-uninitialized warning
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On 10/24/2016 10:57 PM, 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]
>
> 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 and lets us remove two later initializations.
>
> Note that the function is so hard to read that it not only confuses
> the compiler, but also most readers and without this patch it could\
> easily break if one of the 'goto's changed.
>
> Link: https://www.spinics.net/lists/kernel/msg2368133.html
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> mm/shmem.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index ad7813d73ea7..95c4bb690f98 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;
>
> @@ -1835,7 +1834,6 @@ alloc_nohuge: page = shmem_alloc_and_acct_page(gfp, info, sbinfo,
> put_page(page);
> }
> if (error == -ENOSPC && !once++) {
> - info = SHMEM_I(inode);
> spin_lock_irq(&info->lock);
> shmem_recalc_inode(inode);
> spin_unlock_irq(&info->lock);
>

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