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authorAndrea Arcangeli <aarcange@redhat.com>2015-09-05 01:47:08 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2015-09-05 02:54:41 +0300
commitb6ebaedb4cb1a18220ae626c3a9e184ee39dd248 (patch)
tree4ab4d9fda8e406e1103c82325ff7de78c9708816 /mm/userfaultfd.c
parentc1a4de99fada21e2e9251e52cbb51eff5aadc757 (diff)
downloadlinux-b6ebaedb4cb1a18220ae626c3a9e184ee39dd248.tar.xz
userfaultfd: avoid mmap_sem read recursion in mcopy_atomic
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>
Diffstat (limited to 'mm/userfaultfd.c')
-rw-r--r--mm/userfaultfd.c91
1 files changed, 65 insertions, 26 deletions
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index c54c761609fc..77fee9325a57 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -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;
-
- 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);
+ if (!*pagep) {
+ ret = -ENOMEM;
+ page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
+ if (!page)
+ goto out;
+
+ 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 @@ out_release_uncharge_unlock:
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);