Merge tag 'v5.8-rc6' into locking/core, to pick up fixes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 43 insertions, 16 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index f0ae9a6308cb..385759c4ce4b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2028,7 +2028,7 @@ find_page:
 
 		page = find_get_page(mapping, index);
 		if (!page) {
-			if (iocb->ki_flags & IOCB_NOWAIT)
+			if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO))
 				goto would_block;
 			page_cache_sync_readahead(mapping,
 					ra, filp,
@@ -2038,6 +2038,10 @@ find_page:
 				goto no_cached_page;
 		}
 		if (PageReadahead(page)) {
+			if (iocb->ki_flags & IOCB_NOIO) {
+				put_page(page);
+				goto out;
+			}
 			page_cache_async_readahead(mapping,
 					ra, filp, page,
 					index, last_index - index);
@@ -2160,6 +2164,11 @@ page_not_up_to_date_locked:
 		}
 
 readpage:
+		if (iocb->ki_flags & IOCB_NOIO) {
+			unlock_page(page);
+			put_page(page);
+			goto would_block;
+		}
 		/*
 		 * A previous I/O error may have been due to temporary
 		 * failures, eg. multipath errors.
@@ -2249,9 +2258,19 @@ EXPORT_SYMBOL_GPL(generic_file_buffered_read);
  *
  * This is the "read_iter()" routine for all filesystems
  * that can use the page cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall
+ * be returned when no data can be read without waiting for I/O requests
+ * to complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O
+ * requests shall be made for the read or for readahead.  When no data
+ * can be read, -EAGAIN shall be returned.  When readahead would be
+ * triggered, a partial, possibly empty read shall be returned.
+ *
  * Return:
  * * number of bytes copied, even for partial reads
- * * negative error code if nothing was read
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
  */
 ssize_t
 generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
diff --git a/mm/migrate.c b/mm/migrate.c
index f37729673558..40cd7016ae6f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1161,21 +1161,10 @@ out:
 }
 
 /*
- * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move().  Work
- * around it.
- */
-#if defined(CONFIG_ARM) && \
-	defined(GCC_VERSION) && GCC_VERSION < 40900 && GCC_VERSION >= 40700
-#define ICE_noinline noinline
-#else
-#define ICE_noinline
-#endif
-
-/*
  * Obtain the lock on page, remove all ptes and migrate the page
  * to the newly allocated page in newpage.
  */
-static ICE_noinline int unmap_and_move(new_page_t get_new_page,
+static int unmap_and_move(new_page_t get_new_page,
 				   free_page_t put_new_page,
 				   unsigned long private, struct page *page,
 				   int force, enum migrate_mode mode,
diff --git a/mm/mremap.c b/mm/mremap.c
index 5dd572d57ca9..6b153dc05fe4 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -206,9 +206,28 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
 
 	/*
 	 * The destination pmd shouldn't be established, free_pgtables()
-	 * should have release it.
+	 * should have released it.
+	 *
+	 * However, there's a case during execve() where we use mremap
+	 * to move the initial stack, and in that case the target area
+	 * may overlap the source area (always moving down).
+	 *
+	 * If everything is PMD-aligned, that works fine, as moving
+	 * each pmd down will clear the source pmd. But if we first
+	 * have a few 4kB-only pages that get moved down, and then
+	 * hit the "now the rest is PMD-aligned, let's do everything
+	 * one pmd at a time", we will still have the old (now empty
+	 * of any 4kB pages, but still there) PMD in the page table
+	 * tree.
+	 *
+	 * Warn on it once - because we really should try to figure
+	 * out how to do this better - but then say "I won't move
+	 * this pmd".
+	 *
+	 * One alternative might be to just unmap the target pmd at
+	 * this point, and verify that it really is empty. We'll see.
 	 */
-	if (WARN_ON(!pmd_none(*new_pmd)))
+	if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
 		return false;
 
 	/*