Hi Jan,
Thanks for the patch.
The proposed patch should be able to fix the problem, however, do you think it would be a better approach by revising it as:
…
case -EAGAIN:
if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
up_read(&mm->mmap_sem);
return VM_FAULT_RETRY;
}
return VM_FAULT_NOPAGE;
…
This way it can retry fault routine in mm instead of letting CPU have a new fault access.
Thanks,
Jinshan
> On Feb 3, 2017, at 7:07 AM, Jan Kara <jack@xxxxxxx> wrote:
>
> 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.
>
> CC: lustre-devel@xxxxxxxxxxxxxxxx
> CC: cluster-devel@xxxxxxxxxx
> Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> drivers/staging/lustre/lustre/llite/llite_mmap.c | 4 +---
> include/linux/buffer_head.h | 4 +---
> 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;
> }
> --
> 2.10.2
>
> _______________________________________________
> lustre-devel mailing list
> lustre-devel@xxxxxxxxxxxxxxxx
> http://lists.lustre.org/listinfo.cgi/lustre-devel-lustre.org
