Re: [PATCH] xf86drm.c: add counter for ioctl restarting

["Anton V. Boyarshinov" <boyarsh@altlinux.org>]

Hello

> > It seems, that limiting ioctl restarting by some resonable number of trys
> > is a dirty but working way to prevent Xorg lockups.
> 
> And you have audited all callpaths to make sure that they can handle
> EINTR? Up until now it was part of the libdrm api that it did not return
> EINTR...
Speaking strictly no but this code works fine on my Nvidia ION box
with nouveau about a 4 monthes without user-visible problems. It also
have some logging code that shows that all ioctls which have been
restarted more then 5 times are restarting forewer (actually 100
times), but this logging code really unpstreamable.

> From my naive pov, we could just fix the root cause of the bug rather
> than escalating the bug into a random failure.
Yes. This is a dirty trick. But from the user scope, Xorg lockup is a
nasty thing. I have some lockups in a day a year ago, then some bugs
was fixed and a have some lockups in a week. Better, but not so good.
With this patch i have no lockups.

And, from the other side, this patch can be a tool for finding real
bugs if someone add proper logging to if (i don't know the right way to
log problems from libdrm) with ioctl, parameters and restart count.
Users will be able to add this informaition to the bugreports without
accessing by network to locked box.

Regards
Anton