On Mon, Oct 14, 2019 at 06:13:26PM +0200, Johan Hovold wrote: > On Mon, Oct 14, 2019 at 10:48:47AM +0200, Daniel Vetter wrote: > > 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? > > The tty layer depends on this for example when waiting for buffered > writes to complete (something which may never happen when using flow > control). > > > I'm not even sure killable is legit in there, since it's an fd, not a > > process context ... > > It will be run in process context in many cases, and for ttys we're good > AFAICT. Huh, read it a bit, all the ->shutdown callbacks have void return type. But there's indeed interruptible sleeps in there. Doesn't this break userspace that expects that a close() actually flushes the tty? Imo if you're ->release callbacks feels like it should do a wait to guaranteed something userspace expects, then doing a wait_interruptible/killable feels like a bug. Or alternatively, the wait isn't really needed in the first place. > > > 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. > > Yeah, you have a point. > > But take tty again as an example, the close tty operation called from > release() is declared void so there's no propagated return value for vfs > to check. > > It may even be better to fix up the 100 or so callbacks potentially > returning non-zero and make fops->release void so that the compiler > would help us catch any future bugs and also serve as a hint for > developers that returning errnos from fops->release is probably not > what you want to do. > > But that's a lot of churn of course. Hm indeed ->release has int as return type. I guess that's needed for file I/O errno and similar stuff ... Still void return value doesn't catch funny stuff like doing interruptible waits and occasionally failing if you have a process that likes to use signals and also uses some library somewhere to do something. In graphics we have that, with Xorg loving signals for various things. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
