From mboxrd@z Thu Jan 1 00:00:00 1970 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 In-Reply-To: <48BE9AAB.9070303@kernel.org> Message-ID: References: <48BE9AAB.9070303@kernel.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Tejun Heo Cc: linux-mm@kvack.org, Linux Kernel Mailing List , Linus Torvalds , Andrew Morton List-ID: 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 > #include > #include > > #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 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 > --- > 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: -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org