mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers

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>

2 files changed, 2 insertions, 6 deletions

diff --git a/drivers/staging/lustre/lustre/llite/llite_mmap.c b/drivers/staging/lustre/lustre/llite/llite_mmap.c
index ee01f20d8b11..9afa6bec3e6f 100644
--- a/drivers/staging/lustre/lustre/llite/llite_mmap.c
+++ b/drivers/staging/lustre/lustre/llite/llite_mmap.c
@@ -390,15 +390,13 @@ static int ll_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
                 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;
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index d67ab83823ad..79591c3660cc 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -243,12 +243,10 @@ static inline int block_page_mkwrite_return(int err)
 {
         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;
 }