This is a note to let you know that I've just added the patch titled

mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: mm-avoid-returning-vm_fault_retry-from-page_mkwrite-handlers.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Wed Dec 6 16:43:17 CET 2017

From: Jan Kara jack@suse.cz Date: Wed, 8 Feb 2017 14:30:53 -0800 Subject: mm: avoid returning VM_FAULT_RETRY from ->page_mkwrite handlers

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 @@ -402,15 +402,13 @@ 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 @@ -234,12 +234,10 @@ 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; }

Patches currently in stable-queue which might be from jack@suse.cz are

queue-4.4/mm-avoid-returning-vm_fault_retry-from-page_mkwrite-handlers.patch