On Thu, Feb 19, 2026 at 02:17:26PM +0000, Shenwei Wang wrote:
>
>
> > -----Original Message-----
> > From: Andrew Lunn <[email protected]>
> > Sent: Thursday, February 19, 2026 7:27 AM
> > To: Arnaud POULIQUEN <[email protected]>
> > Cc: Shenwei Wang <[email protected]>; Linus Walleij
> > <[email protected]>; Bartosz Golaszewski <[email protected]>; Jonathan Corbet
> > <[email protected]>; Rob Herring <[email protected]>; Krzysztof Kozlowski
> > <[email protected]>; Conor Dooley <[email protected]>; Bjorn Andersson
> > <[email protected]>; Mathieu Poirier <[email protected]>; Frank
> > Li
> > <[email protected]>; Sascha Hauer <[email protected]>; Shuah Khan
> > <[email protected]>; [email protected]; linux-
> > [email protected]; [email protected]; Pengutronix Kernel Team
> > <[email protected]>; Fabio Estevam <[email protected]>; Peng Fan
> > <[email protected]>; [email protected]; linux-
> > [email protected]; [email protected]; linux-arm-
> > [email protected]; dl-linux-imx <[email protected]>; Bartosz
> > Golaszewski <[email protected]>
> > Subject: [EXT] Re: [PATCH v8 3/4] gpio: rpmsg: add generic rpmsg GPIO driver
> >
> > > > + if (sync) {
> > > > + err = wait_for_completion_timeout(&info->cmd_complete,
> > > > +
> > > > msecs_to_jiffies(RPMSG_TIMEOUT));
> > > > + if (err == 0) {
> > > > + dev_err(&info->rpdev->dev, "rpmsg_send timeout!\n");
> > > > + return -ETIMEDOUT;
> > >
> > > strange condition you return an error if err == 0, for redability use
> > > 'ret'
> > > variable or simply:
> > >
> > > if(!wait_for_completion_timeout(&info->cmd_complete,
> > > msecs_to_jiffies(RPMSG_TIMEOUT)) {
> > > dev_err(&info->rpdev->dev, "rpmsg_send timeout!\n");
> > > return -ETIMEDOUT;
> > > }
> >
> > This will be from a comment i made. It appears that
> > do_wait_for_common() can return -ERESTARTSYS. I assume that should be
> > returned to user space?
> >
>
> It looks like there might be a bit of confusion around what
> wait_for_completion_timeout()
> actually returns. That function never returns -ERESTARTSYS. Instead, its
> behavior is pretty
> simple:
>
> - 0 means the wait timed out
> - A positive value means the completion happened (the value is just the
> remaining jiffies)
>
> So the driver returns the timeout error, and the upper application can decide
> how it wants
> to handle that situation, for example restart or ignore.
wait_for_completion_timeout():
return wait_for_common(x, timeout, TASK_UNINTERRUPTIBLE);
wait_for_common():
return __wait_for_common(x, io_schedule_timeout, timeout, state);
__wait_for_common():
timeout = do_wait_for_common(x, action, timeout, state);
...
return timeout;
do_wait_for_common():
do {
if (signal_pending_state(state, current)) {
timeout = -ERESTARTSYS;
break;
}
...
} while (!x->done && timeout);
...
if (!x->done)
return timeout;
...
return timeout ?: 1;
This last line is interesting, and i had to go look at the
documentation:
https://gcc.gnu.org/onlinedocs/gcc/Conditionals.html
So this is equivalent to
return timeout ? timeout : 1;
Hence, it does appear wait_for_completion_timeout() can return
-ERESTARTSYS
There is however a comment in include/linux/errno.h
/*
* These should never be seen by user programs. To return one of ERESTART*
* codes, signal_pending() MUST be set. Note that ptrace can observe these
* at syscall exit tracing, but they will never be left for the debugged user
* process to see.
*/
#define ERESTARTSYS 512
So we do seem to be talking about a corner case, allowing gdb(1) to
know about it, but not user space.
Andrew
