| Message ID | 1479121976-26568-2-git-send-email-david.vrabel@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
>>> On 14.11.16 at 12:12, <david.vrabel@citrix.com> 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. Interesting. I'm pretty sure that back in March/April, when I had to deal with this for our kernels, I was told the upstream kernel is unaffected. In any event I continue to think that https://patchwork.kernel.org/patch/8752901/ is the better (because more generic) solution here. > --- a/drivers/xen/xenbus/xenbus_dev_frontend.c > +++ b/drivers/xen/xenbus/xenbus_dev_frontend.c > @@ -536,6 +536,8 @@ static int xenbus_file_open(struct inode *inode, struct file *filp) > if (xen_store_evtchn == 0) > return -ENOENT; > > + filp->f_mode &= ~FMODE_ATOMIC_POS; /* cdev-style semantics */ > + > nonseekable_open(inode, filp); In any event I think the adjustment should be placed after the call to nonseekable_open(), despite it being unlikely that the function might set the bit again. Jan
diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c index 1e8be12..ce389b4 100644 --- a/drivers/xen/xenbus/xenbus_dev_frontend.c +++ b/drivers/xen/xenbus/xenbus_dev_frontend.c @@ -536,6 +536,8 @@ static int xenbus_file_open(struct inode *inode, struct file *filp) if (xen_store_evtchn == 0) return -ENOENT; + filp->f_mode &= ~FMODE_ATOMIC_POS; /* cdev-style semantics */ + nonseekable_open(inode, filp); u = kzalloc(sizeof(*u), GFP_KERNEL);
/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. Signed-off-by: David Vrabel <david.vrabel@citrix.com> --- drivers/xen/xenbus/xenbus_dev_frontend.c | 2 ++ 1 file changed, 2 insertions(+)