[PATCH] avoid unaligned access when accessing poll stack

Commit 70674f9:

  [PATCH] Optimize select/poll by putting small data sets on the stack

resulted in the poll stack being 4-byte aligned on 64-bit architectures,
causing misaligned accesses to elements in the array.

This patch fixes it by declaring the stack in terms of 'long' instead
of 'char'.

Force alignment of poll and select stacks to long to avoid unaligned
access on 64 bit architectures.

Signed-off-by: Jes Sorensen <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/select.c

@@ -314,7 +314,7 @@ static int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
 	int ret, size, max_fdset;
 	struct fdtable *fdt;
 	/* Allocate small arguments on the stack to save memory and be faster */
-	char stack_fds[SELECT_STACK_ALLOC];
+	long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
 
 	ret = -EINVAL;
 	if (n < 0)
@@ -639,8 +639,10 @@ int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)
  	struct poll_list *walk;
 	struct fdtable *fdt;
 	int max_fdset;
-	/* Allocate small arguments on the stack to save memory and be faster */
-	char stack_pps[POLL_STACK_ALLOC];
+	/* Allocate small arguments on the stack to save memory and be
+	   faster - use long to make sure the buffer is aligned properly
+	   on 64 bit archs to avoid unaligned access */
+	long stack_pps[POLL_STACK_ALLOC/sizeof(long)];
 	struct poll_list *stack_pp = NULL;
 
 	/* Do a sanity check on nfds ... */