Commit 930e652a authored Sep 27, 2006 by David Howells Committed by Linus Torvalds Sep 27, 2006

[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>

parent 0112c4c6

Documentation/nommu-mmap.txt

+10 −0

Original line number	Diff line number	Diff line
		@@ -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
		=============

mm/nommu.c

+9 −5

Original line number	Diff line number	Diff line
		@@ -349,6 +349,15 @@ 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)
		{

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