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>

diff --git a/drivers/staging/lustre/lustre/llite/llite_mmap.c b/drivers/staging/lustre/lustre/llite/llite_mmap.c
index ee01f20d8b1110bec42a3aebf82ef69b79e63d80..9afa6bec3e6f44e22f1bf4fbcbd76e4476348fb3 100644 (file)
--- 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 d67ab83823adc81234b0380feca85877996817db..79591c3660cc1dc61e1e3f4b501c470161c41eb9 100644 (file)
--- 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;
 }