| Message ID | 1541091607-27402-1-git-send-email-miles.chen@mediatek.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4] mm/page_owner: clamp read count to PAGE_SIZE | expand |
On Fri 02-11-18 01:00:07, miles.chen@mediatek.com wrote: > From: Miles Chen <miles.chen@mediatek.com> > > The page owner read might allocate a large size of memory with > a large read count. Allocation fails can easily occur when doing > high order allocations. > > Clamp buffer size to PAGE_SIZE to avoid arbitrary size allocation > and avoid allocation fails due to high order allocation. It is good to mention that interface is root only so the harm due to unbounded allocation request is somehow reduced. I believe we want to use seq_file infrastructure in the long term solution. > Change since v3: > - remove the change in kvmalloc > - keep kmalloc in page_owner.c > > Change since v2: > - improve kvmalloc, allow sub page allocations fallback to > vmalloc when CONFIG_HIGHMEM=y > > Change since v1: > - use kvmalloc() > - clamp buffer size to PAGE_SIZE > > Signed-off-by: Miles Chen <miles.chen@mediatek.com> > Cc: Joe Perches <joe@perches.com> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Michal Hocko <mhocko@kernel.org> Acked-by: Michal Hocko <mhocko@suse.com> Thanks! > --- > mm/page_owner.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/page_owner.c b/mm/page_owner.c > index 87bc0dfdb52b..b83f295e4eca 100644 > --- a/mm/page_owner.c > +++ b/mm/page_owner.c > @@ -351,6 +351,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, > .skip = 0 > }; > > + count = count > PAGE_SIZE ? PAGE_SIZE : count; > kbuf = kmalloc(count, GFP_KERNEL); > if (!kbuf) > return -ENOMEM; > -- > 2.18.0 >
On Fri, 2 Nov 2018 01:00:07 +0800 <miles.chen@mediatek.com> wrote: > From: Miles Chen <miles.chen@mediatek.com> > > The page owner read might allocate a large size of memory with > a large read count. Allocation fails can easily occur when doing > high order allocations. > > Clamp buffer size to PAGE_SIZE to avoid arbitrary size allocation > and avoid allocation fails due to high order allocation. > > ... > > --- a/mm/page_owner.c > +++ b/mm/page_owner.c > @@ -351,6 +351,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, > .skip = 0 > }; > > + count = count > PAGE_SIZE ? PAGE_SIZE : count; > kbuf = kmalloc(count, GFP_KERNEL); > if (!kbuf) > return -ENOMEM; A bit tidier: --- a/mm/page_owner.c~mm-page_owner-clamp-read-count-to-page_size-fix +++ a/mm/page_owner.c @@ -351,7 +351,7 @@ print_page_owner(char __user *buf, size_ .skip = 0 }; - count = count > PAGE_SIZE ? PAGE_SIZE : count; + count = min_t(size_t, count, PAGE_SIZE); kbuf = kmalloc(count, GFP_KERNEL); if (!kbuf) return -ENOMEM;
On Thu, 2018-11-01 at 14:47 -0700, Andrew Morton wrote: > On Fri, 2 Nov 2018 01:00:07 +0800 <miles.chen@mediatek.com> wrote: > > > From: Miles Chen <miles.chen@mediatek.com> > > > > The page owner read might allocate a large size of memory with > > a large read count. Allocation fails can easily occur when doing > > high order allocations. > > > > Clamp buffer size to PAGE_SIZE to avoid arbitrary size allocation > > and avoid allocation fails due to high order allocation. > > > > ... > > > > --- a/mm/page_owner.c > > +++ b/mm/page_owner.c > > @@ -351,6 +351,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, > > .skip = 0 > > }; > > > > + count = count > PAGE_SIZE ? PAGE_SIZE : count; > > kbuf = kmalloc(count, GFP_KERNEL); > > if (!kbuf) > > return -ENOMEM; > > A bit tidier: > > --- a/mm/page_owner.c~mm-page_owner-clamp-read-count-to-page_size-fix > +++ a/mm/page_owner.c > @@ -351,7 +351,7 @@ print_page_owner(char __user *buf, size_ > .skip = 0 > }; > > - count = count > PAGE_SIZE ? PAGE_SIZE : count; > + count = min_t(size_t, count, PAGE_SIZE); > kbuf = kmalloc(count, GFP_KERNEL); > if (!kbuf) > return -ENOMEM; A bit tidier still might be if (count > PAGE_SIZE) count = PAGE_SIZE; as that would not always cause a write back to count.
On Thu, Nov 01, 2018 at 04:30:12PM -0700, Joe Perches wrote: > On Thu, 2018-11-01 at 14:47 -0700, Andrew Morton wrote: > > +++ a/mm/page_owner.c > > @@ -351,7 +351,7 @@ print_page_owner(char __user *buf, size_ > > .skip = 0 > > }; > > > > - count = count > PAGE_SIZE ? PAGE_SIZE : count; > > + count = min_t(size_t, count, PAGE_SIZE); > > kbuf = kmalloc(count, GFP_KERNEL); > > if (!kbuf) > > return -ENOMEM; > > A bit tidier still might be > > if (count > PAGE_SIZE) > count = PAGE_SIZE; > > as that would not always cause a write back to count. 90% chance 'count' is already in a register and will stay there. 99.9% chance that if it's not in a register, it's on the top of the stack, which is by definition a hot, local, dirty cacheline. What you're saying makes sense for a struct which might well be in a shared cacheline state. But for a function-local variable? No.
> On Nov 1, 2018, at 3:47 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > > - count = count > PAGE_SIZE ? PAGE_SIZE : count; > + count = min_t(size_t, count, PAGE_SIZE); > kbuf = kmalloc(count, GFP_KERNEL); > if (!kbuf) > return -ENOMEM; Is the use of min_t vs. the C conditional mostly to be more self-documenting? The compiler-generated assembly between the two versions seems mostly a wash. William Kucharski
On Thu, 1 Nov 2018 18:41:33 -0600 William Kucharski <william.kucharski@oracle.com> wrote: > > > > On Nov 1, 2018, at 3:47 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > > > > - count = count > PAGE_SIZE ? PAGE_SIZE : count; > > + count = min_t(size_t, count, PAGE_SIZE); > > kbuf = kmalloc(count, GFP_KERNEL); > > if (!kbuf) > > return -ENOMEM; > > Is the use of min_t vs. the C conditional mostly to be more self-documenting? Yup. It saves the reader from having to parse the code to figure out "this is a min operation".
diff --git a/mm/page_owner.c b/mm/page_owner.c index 87bc0dfdb52b..b83f295e4eca 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -351,6 +351,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, .skip = 0 }; + count = count > PAGE_SIZE ? PAGE_SIZE : count; kbuf = kmalloc(count, GFP_KERNEL); if (!kbuf) return -ENOMEM;