Re: [PATCH 0/4] treewide: fix interrupted release

From: Daniel Vetter
Date: Mon Oct 14 2019 - 04:48:54 EST

On Fri, Oct 11, 2019 at 11:36:33AM +0200, Johan Hovold wrote:
> On Thu, Oct 10, 2019 at 03:50:43PM +0200, Daniel Vetter wrote:
> > On Thu, Oct 10, 2019 at 03:13:29PM +0200, Johan Hovold wrote:
> > > Two old USB drivers had a bug in them which could lead to memory leaks
> > > if an interrupted process raced with a disconnect event.
> > >
> > > Turns out we had a few more driver in other subsystems with the same
> > > kind of bug in them.
> > Random funny idea: Could we do some debug annotations (akin to
> > might_sleep) that splats when you might_sleep_interruptible somewhere
> > where interruptible sleeps are generally a bad idea? Like in
> > fops->release?
> There's nothing wrong with interruptible sleep in fops->release per se,
> it's just that drivers cannot return -ERESTARTSYS and friends and expect
> to be called again later.

Do you have a legit usecase for interruptible sleeps in fops->release?

I'm not even sure killable is legit in there, since it's an fd, not a
process context ...

> The return value from release() is ignored by vfs, and adding a splat in
> __fput() to catch these buggy drivers might be overkill.

Ime once you have a handful of instances of a broken pattern, creating a
check for it (under a debug option only ofc) is very much justified.
Otherwise they just come back to life like the undead, all the time. And
there's a _lot_ of fops->release callbacks in the kernel.
Daniel Vetter
Software Engineer, Intel Corporation