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Subject[PATCH 3.18 16/26] mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers
Date
3.18-stable review patch.  If anyone has any objections, please let me know.

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

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
@@ -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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