Merge drm/drm-next into drm-misc-next

Backmerging to get v6.1-rc6 into drm-misc-next.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

1 files changed, 22 insertions, 5 deletions

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index e24e8a47ce8a..650ab6cfd5f4 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -64,7 +64,7 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
 	pte_t _dst_pte, *dst_pte;
 	bool writable = dst_vma->vm_flags & VM_WRITE;
 	bool vm_shared = dst_vma->vm_flags & VM_SHARED;
-	bool page_in_cache = page->mapping;
+	bool page_in_cache = page_mapping(page);
 	spinlock_t *ptl;
 	struct inode *inode;
 	pgoff_t offset, max_off;
@@ -157,11 +157,28 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 		if (!page)
 			goto out;
 
-		page_kaddr = kmap_atomic(page);
+		page_kaddr = kmap_local_page(page);
+		/*
+		 * The read mmap_lock is held here.  Despite the
+		 * mmap_lock being read recursive a deadlock is still
+		 * possible if a writer has taken a lock.  For example:
+		 *
+		 * process A thread 1 takes read lock on own mmap_lock
+		 * process A thread 2 calls mmap, blocks taking write lock
+		 * process B thread 1 takes page fault, read lock on own mmap lock
+		 * process B thread 2 calls mmap, blocks taking write lock
+		 * process A thread 1 blocks taking read lock on process B
+		 * process B thread 1 blocks taking read lock on process A
+		 *
+		 * Disable page faults to prevent potential deadlock
+		 * and retry the copy outside the mmap_lock.
+		 */
+		pagefault_disable();
 		ret = copy_from_user(page_kaddr,
 				     (const void __user *) src_addr,
 				     PAGE_SIZE);
-		kunmap_atomic(page_kaddr);
+		pagefault_enable();
+		kunmap_local(page_kaddr);
 
 		/* fallback to copy_from_user outside mmap_lock */
 		if (unlikely(ret)) {
@@ -646,11 +663,11 @@ retry:
 			mmap_read_unlock(dst_mm);
 			BUG_ON(!page);
 
-			page_kaddr = kmap(page);
+			page_kaddr = kmap_local_page(page);
 			err = copy_from_user(page_kaddr,
 					     (const void __user *) src_addr,
 					     PAGE_SIZE);
-			kunmap(page);
+			kunmap_local(page_kaddr);
 			if (unlikely(err)) {
 				err = -EFAULT;
 				goto out;