Patch "mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

    mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-avoid-returning-vm_fault_retry-from-page_mkwrite-handlers.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Wed, 8 Feb 2017 14:30:53 -0800
Subject: mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers

From: Jan Kara <[email protected]>

[ Upstream commit 0911d0041c22922228ca52a977d7b0b0159fee4b ]

Some ->page_mkwrite handlers may return VM_FAULT_RETRY as its return code (GFS2 or Lustre can definitely do this). However VM_FAULT_RETRY from ->page_mkwrite is completely unhandled by the mm code and results in locking and writeably mapping the page which definitely is not what the caller wanted.

Fix Lustre and block_page_mkwrite_ret() used by other filesystems (notably GFS2) to return VM_FAULT_NOPAGE instead which results in bailing out from the fault code, the CPU then retries the access, and we fault again effectively doing what the handler wanted.

---
 drivers/staging/lustre/lustre/llite/llite_mmap.c |    4 +---
 include/linux/buffer_head.h                      |    4 +---
 2 files changed, 2 insertions(+), 6 deletions(-)

@@ -401,15 +401,13 @@ static int ll_page_mkwrite(struct vm_are
 		result = VM_FAULT_LOCKED;
 		break;
 	case -ENODATA:
+	case -EAGAIN:
 	case -EFAULT:
 		result = VM_FAULT_NOPAGE;
 		break;
 	case -ENOMEM:
 		result = VM_FAULT_OOM;
 		break;
-	case -EAGAIN:
-		result = VM_FAULT_RETRY;
-		break;
 	default:
 		result = VM_FAULT_SIGBUS;
 		break;

@@ -239,12 +239,10 @@ static inline int block_page_mkwrite_ret
 {
 	if (err == 0)
 		return VM_FAULT_LOCKED;
-	if (err == -EFAULT)
+	if (err == -EFAULT || err == -EAGAIN)
 		return VM_FAULT_NOPAGE;
 	if (err == -ENOMEM)
 		return VM_FAULT_OOM;
-	if (err == -EAGAIN)
-		return VM_FAULT_RETRY;
 	/* -ENOSPC, -EDQUOT, -EIO ... */
 	return VM_FAULT_SIGBUS;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mm-avoid-returning-vm_fault_retry-from-page_mkwrite-handlers.patch queue-4.9/dax-avoid-page-invalidation-races-and-unnecessary-radix-tree-traversals.patch