[PATCH] NOMMU: Make futexes work under NOMMU conditions

Make futexes work under NOMMU conditions.

This can be tested by running this in one shell:

	#define SYSERROR(X, Y) \
		do { if ((long)(X) == -1L) { perror(Y); exit(1); }} while(0)

	int main()
	{
		int shmid, tmp, *f, n;

		shmid = shmget(23, 4, IPC_CREAT|0666);
		SYSERROR(shmid, "shmget");

		f = shmat(shmid, NULL, 0);
		SYSERROR(f, "shmat");

		n = *f;
		printf("WAIT: %p{%x}\n", f, n);
		tmp = futex(f, FUTEX_WAIT, n, NULL, NULL, 0);
		SYSERROR(tmp, "futex");
		printf("WAITED: %d\n", tmp);

		tmp = shmdt(f);
		SYSERROR(tmp, "shmdt");

		exit(0);
	}

And then this in the other shell:

	#define SYSERROR(X, Y) \
		do { if ((long)(X) == -1L) { perror(Y); exit(1); }} while(0)

	int main()
	{
		int shmid, tmp, *f;

		shmid = shmget(23, 4, IPC_CREAT|0666);
		SYSERROR(shmid, "shmget");

		f = shmat(shmid, NULL, 0);
		SYSERROR(f, "shmat");

		(*f)++;
		printf("WAKE: %p{%x}\n", f, *f);
		tmp = futex(f, FUTEX_WAKE, 1, NULL, NULL, 0);
		SYSERROR(tmp, "futex");
		printf("WOKE: %d\n", tmp);

		tmp = shmdt(f);
		SYSERROR(tmp, "shmdt");

		exit(0);
	}

The first program will set up a SYSV IPC SHM segment and wait on a futex in it
for the number at the start to change.  The program will increment that number
and wake the first program up.  This leads to output of the form:

	SHELL 1			SHELL 2
	=======================	=======================
	# /dowait
	WAIT: 0xc32ac000{0}
				# /dowake
				WAKE: 0xc32ac000{1}
	WAITED: 0		WOKE: 1

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 19 insertions, 5 deletions

diff --git a/Documentation/nommu-mmap.txt b/Documentation/nommu-mmap.txt
index 4db7c18bf68c..7714f57caad5 100644
--- a/Documentation/nommu-mmap.txt
+++ b/Documentation/nommu-mmap.txt
@@ -138,6 +138,16 @@ mode.  The former through the usual mechanism, the latter through files created
 on ramfs or tmpfs mounts.
 
 
+=======
+FUTEXES
+=======
+
+Futexes are supported in NOMMU mode if the arch supports them.  An error will
+be given if an address passed to the futex system call lies outside the
+mappings made by a process or if the mapping in which the address lies does not
+support futexes (such as an I/O chardev mapping).
+
+
 =============
 NO-MMU MREMAP
 =============
diff --git a/mm/nommu.c b/mm/nommu.c
index 23cfa8ec914a..564540662192 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -350,6 +350,15 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 EXPORT_SYMBOL(find_vma);
 
 /*
+ * find a VMA
+ * - we don't extend stack VMAs under NOMMU conditions
+ */
+struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)
+{
+        return find_vma(mm, addr);
+}
+
+/*
  * look up the first VMA exactly that exactly matches addr
  * - should be called with mm->mmap_sem at least held readlocked
  */
@@ -1153,11 +1162,6 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
         return NULL;
 }
 
-struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)
-{
-        return NULL;
-}
-
 int remap_pfn_range(struct vm_area_struct *vma, unsigned long from,
                 unsigned long to, unsigned long size, pgprot_t prot)
 {