mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers
authorJan Kara <jack@suse.cz>
Wed, 8 Feb 2017 22:30:53 +0000 (14:30 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 8 Feb 2017 23:41:43 +0000 (15:41 -0800)
commit0911d0041c22922228ca52a977d7b0b0159fee4b
treeecd0e2bd3ec2f1e934409a43dd3b0798860c7d8b
parented5bd7dc88edf4a4a9c67130742b1b59aa017a5f
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>
drivers/staging/lustre/lustre/llite/llite_mmap.c
include/linux/buffer_head.h