Re: [Xen-devel] [PATCHv6] xenbus: fix deadlock on writes to /proc/xen/xenbus

[Juergen Gross <jgross@xxxxxxxx>]

On 09/12/16 15:41, David Vrabel wrote:
> /proc/xen/xenbus does not work correctly.  A read blocked waiting for
> a xenstore message holds the mutex needed for atomic file position
> updates.  This blocks any writes on the same file handle, which can
> deadlock if the write is needed to unblock the read.
> 
> Clear FMODE_ATOMIC_POS when opening this device to always get
> character device like sematics.

"semantics". I can fix this when committing.

> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

> ---
> v6:
> - clear flag after calling nonseekable_open().
> ---
>  drivers/xen/xenbus/xenbus_dev_frontend.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c 
> b/drivers/xen/xenbus/xenbus_dev_frontend.c
> index 1e8be12..6c0ead4 100644
> --- a/drivers/xen/xenbus/xenbus_dev_frontend.c
> +++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
> @@ -538,6 +538,8 @@ static int xenbus_file_open(struct inode *inode, struct 
> file *filp)
>  
>       nonseekable_open(inode, filp);
>  
> +     filp->f_mode &= ~FMODE_ATOMIC_POS; /* cdev-style semantics */
> +
>       u = kzalloc(sizeof(*u), GFP_KERNEL);
>       if (u == NULL)
>               return -ENOMEM;
> 


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