From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f177.google.com (mail-ob0-f177.google.com [209.85.214.177]) by kanga.kvack.org (Postfix) with ESMTP id E28146B025B for ; Mon, 14 Sep 2015 09:22:30 -0400 (EDT) Received: by obbzf10 with SMTP id zf10so52448517obb.2 for ; Mon, 14 Sep 2015 06:22:30 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id q126si1889685oia.45.2015.09.14.06.22.29 for ; Mon, 14 Sep 2015 06:22:30 -0700 (PDT) Date: Mon, 14 Sep 2015 14:22:30 +0100 From: Will Deacon Subject: Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file VMAs have ->vm_ops set") Message-ID: <20150914132230.GD23878@arm.com> References: <20150914105346.GB23878@arm.com> <20150914115800.06242CE@black.fi.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150914115800.06242CE@black.fi.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: "oleg@redhat.com" , "hpa@zytor.com" , "luto@amacapital.net" , "dave.hansen@linux.intel.com" , "mingo@elte.hu" , "minchan@kernel.org" , "tglx@linutronix.de" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" On Mon, Sep 14, 2015 at 12:57:59PM +0100, Kirill A. Shutemov wrote: > Will Deacon wrote: > > Your patch 6dc296e7df4c ("mm: make sure all file VMAs have ->vm_ops set") > > causes some mmap regressions in LTP, which appears to use a MAP_PRIVATE > > mmap of /dev/zero as a way to get anonymous pages in some of its tests > > (specifically mmap10 [1]). > > > > Dead simple reproducer below. Is this change in behaviour intentional? > > Ouch. Of couse it's a bug. > > Fix is below. I don't really like it, but I cannot find any better > solution. Brill, thanks for the quick response! I agree that the fix isn't very nice. Maybe moving the mmap_zero test into a helper would make it more palatable? > From 97be4458fd63758b0c233e528bf952d1cd26428e Mon Sep 17 00:00:00 2001 > From: "Kirill A. Shutemov" > Date: Mon, 14 Sep 2015 14:44:32 +0300 > Subject: [PATCH] mm: fix mmap(MAP_PRIVATE) on /dev/zero > > In attempt to make mm less fragile I've screwed up setting up anonymous > mappings by mmap() on /dev/zero. > > Here's the fix. > > Signed-off-by: Kirill A. Shutemov > Fixes: 6dc296e7df4c ("mm: make sure all file VMAs have ->vm_ops set") > Reported-by: Will Deacon FWIW: Tested-by: Will Deacon Cheers, Will > --- > drivers/char/mem.c | 2 +- > include/linux/mm.h | 1 + > mm/mmap.c | 6 ++++-- > 3 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/drivers/char/mem.c b/drivers/char/mem.c > index 6b1721f978c2..c8fe3af4de29 100644 > --- a/drivers/char/mem.c > +++ b/drivers/char/mem.c > @@ -651,7 +651,7 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter) > return written; > } > > -static int mmap_zero(struct file *file, struct vm_area_struct *vma) > +int mmap_zero(struct file *file, struct vm_area_struct *vma) > { > #ifndef CONFIG_MMU > return -ENOSYS; > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 91c08f6f0dc9..5e152e9588ec 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1066,6 +1066,7 @@ extern void pagefault_out_of_memory(void); > extern void show_free_areas(unsigned int flags); > extern bool skip_free_areas_node(unsigned int flags, int nid); > > +int mmap_zero(struct file *file, struct vm_area_struct *vma); > int shmem_zero_setup(struct vm_area_struct *); > #ifdef CONFIG_SHMEM > bool shmem_mapping(struct address_space *mapping); > diff --git a/mm/mmap.c b/mm/mmap.c > index 971dd2cb77d2..7960fd206a2f 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -612,7 +612,9 @@ static unsigned long count_vma_pages_range(struct mm_struct *mm, > void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma, > struct rb_node **rb_link, struct rb_node *rb_parent) > { > - WARN_ONCE(vma->vm_file && !vma->vm_ops, "missing vma->vm_ops"); > + WARN_ONCE(vma->vm_file && !vma->vm_ops && > + vma->vm_file->f_op->mmap != mmap_zero, > + "missing vma->vm_ops"); > > /* Update tracking information for the gap following the new vma. */ > if (vma->vm_next) > @@ -1639,7 +1641,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > WARN_ON_ONCE(addr != vma->vm_start); > > /* All file mapping must have ->vm_ops set */ > - if (!vma->vm_ops) { > + if (!vma->vm_ops && file->f_op->mmap != &mmap_zero) { > static const struct vm_operations_struct dummy_ops = {}; > vma->vm_ops = &dummy_ops; > } > -- > 2.5.1 > -- 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