Patch "mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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 4.4-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-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Dec  6 16:43:17 CET 2017
From: Jan Kara <jack@suse.cz>
Date: Wed, 8 Feb 2017 14:30:53 -0800
Subject: mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers

From: Jan Kara <jack@suse.cz>


[ 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.

Link: http://lkml.kernel.org/r/20170203150729.15863-1-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/staging/lustre/lustre/llite/llite_mmap.c |    4 +---
 include/linux/buffer_head.h                      |    4 +---
 2 files changed, 2 insertions(+), 6 deletions(-)

--- a/drivers/staging/lustre/lustre/llite/llite_mmap.c
+++ b/drivers/staging/lustre/lustre/llite/llite_mmap.c
@@ -402,15 +402,13 @@ 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;
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -234,12 +234,10 @@ 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 jack@suse.cz are

queue-4.4/mm-avoid-returning-vm_fault_retry-from-page_mkwrite-handlers.patch