Messages in this thread | | | Date | Wed, 3 Sep 2008 17:25:02 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [PATCH #2.6.27-rc5] mmap: fix petty bug in anonymous shared mmap offset handling |
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On Wed, 3 Sep 2008, Tejun Heo wrote:
> Anonymous mappings should ignore offset but shared anonymous mapping > forgot to clear it and makes the following legit test program trigger > SIGBUS. > > #include <sys/mman.h> > #include <stdio.h> > #include <errno.h> > > #define PAGE_SIZE 4096 > > int main(void) > { > char *p; > int i; > > p = mmap(NULL, 2 * PAGE_SIZE, PROT_READ|PROT_WRITE, > MAP_SHARED|MAP_ANONYMOUS, -1, PAGE_SIZE); > if (p == MAP_FAILED) { > perror("mmap"); > return 1; > } > > for (i = 0; i < 2; i++) { > printf("page %d\n", i); > p[i * 4096] = i; > } > return 0; > } > > Fix it. > > Signed-off-by: Tejun Heo <tj@kernel.org>
Fair enough. The current behaviour has (almost) never bothered us, so I'm uncertain if your test is legit, but I can't see any reason to object to the change. Particularly since (just out of sight below the context of your patch) we force pgoff in the MAP_PRIVATE case.
Acked-by: Hugh Dickins <hugh@veritas.com>
> --- > mm/mmap.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 339cf5c..e7a5a68 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1030,6 +1030,10 @@ unsigned long do_mmap_pgoff(struct file * file, unsigned long addr, > } else { > switch (flags & MAP_TYPE) { > case MAP_SHARED: > + /* > + * Ignore pgoff. > + */ > + pgoff = 0; > vm_flags |= VM_SHARED | VM_MAYSHARE; > break; > case MAP_PRIVATE:
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