3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <j...@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-j...@suse.cz
Signed-off-by: Jan Kara <j...@suse.cz>
Reported-by: Al Viro <v...@zeniv.linux.org.uk>
Reviewed-by: Jinshan Xiong <jinshan.xi...@intel.com>
Cc: Matthew Wilcox <wi...@infradead.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.le...@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gre...@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
@@ -407,15 +407,13 @@ 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
@@ -236,12 +236,10 @@ 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;
 }


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