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userfaultfd: avoid mmap_sem read recursion in mcopy_atomic

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If the rwsem starves writers it wasn't strictly a bug but lockdep
doesn't like it and this avoids depending on lowlevel implementation
details of the lock.

[akpm@linux-foundation.org: delete weird BUILD_BUG_ON()]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Sanidhya Kashyap <sanidhya.gatech@gmail.com>
Cc: zhang.zhanghailiang@huawei.com
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Feiner <pfeiner@google.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Huangpeng (Peter)" <peter.huangpeng@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2015-09-04 15:47:08 -07:00 committed by Linus Torvalds
parent c1a4de99fa
commit b6ebaedb4c
1 changed files with 64 additions and 25 deletions
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89
mm/userfaultfd.c
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@ -21,26 +21,39 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr)
unsigned long src_addr,
struct page **pagep)
{
struct mem_cgroup *memcg;
pte_t _dst_pte, *dst_pte;
spinlock_t *ptl;
struct page *page;
void *page_kaddr;
int ret;
struct page *page;
ret = -ENOMEM;
page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
if (!page)
goto out;
if (!*pagep) {
ret = -ENOMEM;
page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
if (!page)
goto out;
page_kaddr = kmap(page);
ret = -EFAULT;
if (copy_from_user(page_kaddr, (const void __user *) src_addr,
PAGE_SIZE))
goto out_kunmap_release;
kunmap(page);
page_kaddr = kmap_atomic(page);
ret = copy_from_user(page_kaddr,
(const void __user *) src_addr,
PAGE_SIZE);
kunmap_atomic(page_kaddr);
/* fallback to copy_from_user outside mmap_sem */
if (unlikely(ret)) {
ret = -EFAULT;
*pagep = page;
/* don't free the page */
goto out;
}
} else {
page = *pagep;
*pagep = NULL;
}
/*
* The memory barrier inside __SetPageUptodate makes sure that
@ -82,9 +95,6 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
out_release:
page_cache_release(page);
goto out;
out_kunmap_release:
kunmap(page);
goto out_release;
}
static int mfill_zeropage_pte(struct mm_struct *dst_mm,
@ -139,7 +149,8 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
ssize_t err;
pmd_t *dst_pmd;
unsigned long src_addr, dst_addr;
long copied = 0;
long copied;
struct page *page;
/*
* Sanitize the command parameters:
@ -151,6 +162,11 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
BUG_ON(src_start + len <= src_start);
BUG_ON(dst_start + len <= dst_start);
src_addr = src_start;
dst_addr = dst_start;
copied = 0;
page = NULL;
retry:
down_read(&dst_mm->mmap_sem);
/*
@ -160,10 +176,10 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
err = -EINVAL;
dst_vma = find_vma(dst_mm, dst_start);
if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
goto out;
goto out_unlock;
if (dst_start < dst_vma->vm_start ||
dst_start + len > dst_vma->vm_end)
goto out;
goto out_unlock;
/*
* Be strict and only allow __mcopy_atomic on userfaultfd
@ -175,14 +191,14 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
* belonging to the userfaultfd and not syscalls.
*/
if (!dst_vma->vm_userfaultfd_ctx.ctx)
goto out;
goto out_unlock;
/*
* FIXME: only allow copying on anonymous vmas, tmpfs should
* be added.
*/
if (dst_vma->vm_ops)
goto out;
goto out_unlock;
/*
* Ensure the dst_vma has a anon_vma or this page
@ -191,12 +207,13 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
*/
err = -ENOMEM;
if (unlikely(anon_vma_prepare(dst_vma)))
goto out;
goto out_unlock;
for (src_addr = src_start, dst_addr = dst_start;
src_addr < src_start + len; ) {
while (src_addr < src_start + len) {
pmd_t dst_pmdval;
BUG_ON(dst_addr >= dst_start + len);
dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
if (unlikely(!dst_pmd)) {
err = -ENOMEM;
@ -229,13 +246,32 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
if (!zeropage)
err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
dst_addr, src_addr);
dst_addr, src_addr, &page);
else
err = mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma,
dst_addr);
cond_resched();
if (unlikely(err == -EFAULT)) {
void *page_kaddr;
up_read(&dst_mm->mmap_sem);
BUG_ON(!page);
page_kaddr = kmap(page);
err = copy_from_user(page_kaddr,
(const void __user *) src_addr,
PAGE_SIZE);
kunmap(page);
if (unlikely(err)) {
err = -EFAULT;
goto out;
}
goto retry;
} else
BUG_ON(page);
if (!err) {
dst_addr += PAGE_SIZE;
src_addr += PAGE_SIZE;
@ -248,8 +284,11 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
break;
}
out:
out_unlock:
up_read(&dst_mm->mmap_sem);
out:
if (page)
page_cache_release(page);
BUG_ON(copied < 0);
BUG_ON(err > 0);
BUG_ON(!copied && !err);