Commit 61609d01 authored by Yuri Tikhonov's avatar Yuri Tikhonov Committed by Linus Torvalds

shmem: fix division by zero

Fix a division by zero which we have in shmem_truncate_range() and
shmem_unuse_inode() when using big PAGE_SIZE values (e.g.  256kB on
ppc44x).

With 256kB PAGE_SIZE, the ENTRIES_PER_PAGEPAGE constant becomes too large
(0x1.0000.0000) on a 32-bit kernel, so this patch just changes its type
from 'unsigned long' to 'unsigned long long'.

Hugh: reverted its unsigned long longs in shmem_truncate_range() and
shmem_getpage(): the pagecache index cannot be more than an unsigned long,
so the divisions by zero occurred in unreached code.  It's a pity we need
any ULL arithmetic here, but I found no pretty way to avoid it.
Signed-off-by: default avatarYuri Tikhonov <yur@emcraft.com>
Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 347486bb
...@@ -66,7 +66,7 @@ static struct vfsmount *shm_mnt; ...@@ -66,7 +66,7 @@ static struct vfsmount *shm_mnt;
#include <asm/pgtable.h> #include <asm/pgtable.h>
#define ENTRIES_PER_PAGE (PAGE_CACHE_SIZE/sizeof(unsigned long)) #define ENTRIES_PER_PAGE (PAGE_CACHE_SIZE/sizeof(unsigned long))
#define ENTRIES_PER_PAGEPAGE (ENTRIES_PER_PAGE*ENTRIES_PER_PAGE) #define ENTRIES_PER_PAGEPAGE ((unsigned long long)ENTRIES_PER_PAGE*ENTRIES_PER_PAGE)
#define BLOCKS_PER_PAGE (PAGE_CACHE_SIZE/512) #define BLOCKS_PER_PAGE (PAGE_CACHE_SIZE/512)
#define SHMEM_MAX_INDEX (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * (ENTRIES_PER_PAGE+1)) #define SHMEM_MAX_INDEX (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * (ENTRIES_PER_PAGE+1))
......
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