mirror of
https://github.com/torvalds/linux.git
synced 2026-07-06 21:32:20 +02:00
f69061bedd
With the previous patch the state transition handling of the reset code itself is now (hopefully) race free and solid. But that still leaves out everyone else - with the various lock-free wait paths we have there's the possibility that the reset happens between the point where we read the seqno we should wait on and the actual wait. And if __wait_seqno then never sees the RESET_IN_PROGRESS state, we'll happily wait for a seqno which will in all likelyhood never signal. In practice this is not a big problem since the X server gets constantly interrupted, and can then submit more work (hopefully) to unblock everyone else: As soon as a new seqno write lands, all waiters will unblock. But running the i-g-t reset testcase ZZ_hangman can expose this race, especially on slower hw with fewer cpu cores. Now looking forward to ARB_robustness and friends that's not the best possible behaviour, hence this patch adds a reset_counter to be able to detect any reset, even if a given thread never observed the in-progress state. The important part is to correctly order things: - The write side needs to increment the counter after any seqno gets reset. Hence we need to do that at the end of the reset work, and again wake everyone up. We also need to place a barrier in between any possible seqno changes and the counter increment, since any unlock operations only guarantee that nothing leaks out, but not that at later load operation gets moved ahead. - On the read side we need to ensure that no reset can sneak in and invalidate the seqno. In all cases we can use the one-sided barrier that unlock operations guarantee (of the lock protecting the respective seqno/ring pair) to ensure correct ordering. Hence it is sufficient to place the atomic read before the mutex/spin_unlock and no additional barriers are required. The end-result of all this is that we need to wake up everyone twice in a reset operation: - First, before the reset starts, to get any lockholders of the locks, so that the reset can proceed. - Second, after the reset is completed, to allow waiters to properly and reliably detect the reset condition and bail out. I admit that this entire reset_counter thing smells a bit like overkill, but I think it's justified since it makes it really explicit what the bail-out condition is. And we need a reset counter anyway to implement ARB_robustness, and imo with finer-grained locking on the horizont this is the most resilient scheme I could think of. v2: Drop spurious change in the wait_for_error EXIT_COND - we only need to wait until we leave the reset-in-progress wedged state. v3: Don't play tricks with barriers in the throttle ioctl, the spin_unlock is barrier enough. I've also considered using a little helper to grab the current reset_counter, but then decided that hiding the atomic_read isn't a great idea, since having it explicitly show up in the code is a nice remainder to reviews to check the memory barriers. v4: Add a comment to explain why we need to fall through in __wait_seqno in the end variable assignments. v5: Review from Damien: - s/smb/smp/ in a comment - don't increment the reset counter after we've set it to WEDGED. Now we (again) properly wedge the gpu when the reset fails. Reviewed-by: Damien Lespiau <damien.lespiau@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> |
||
|---|---|---|
| .. | ||
| accessibility | ||
| acpi | ||
| amba | ||
| ata | ||
| atm | ||
| auxdisplay | ||
| base | ||
| bcma | ||
| block | ||
| bluetooth | ||
| bus | ||
| cdrom | ||
| char | ||
| clk | ||
| clocksource | ||
| connector | ||
| cpufreq | ||
| cpuidle | ||
| crypto | ||
| dca | ||
| devfreq | ||
| dio | ||
| dma | ||
| edac | ||
| eisa | ||
| extcon | ||
| firewire | ||
| firmware | ||
| gpio | ||
| gpu | ||
| hid | ||
| hsi | ||
| hv | ||
| hwmon | ||
| hwspinlock | ||
| i2c | ||
| ide | ||
| idle | ||
| iio | ||
| infiniband | ||
| input | ||
| iommu | ||
| ipack | ||
| irqchip | ||
| isdn | ||
| leds | ||
| lguest | ||
| macintosh | ||
| md | ||
| media | ||
| memory | ||
| memstick | ||
| message | ||
| mfd | ||
| misc | ||
| mmc | ||
| mtd | ||
| net | ||
| nfc | ||
| nubus | ||
| of | ||
| oprofile | ||
| parisc | ||
| parport | ||
| pci | ||
| pcmcia | ||
| pinctrl | ||
| platform | ||
| pnp | ||
| power | ||
| pps | ||
| ps3 | ||
| ptp | ||
| pwm | ||
| rapidio | ||
| regulator | ||
| remoteproc | ||
| rpmsg | ||
| rtc | ||
| s390 | ||
| sbus | ||
| scsi | ||
| sfi | ||
| sh | ||
| sn | ||
| spi | ||
| ssb | ||
| staging | ||
| target | ||
| tc | ||
| thermal | ||
| tty | ||
| uio | ||
| usb | ||
| uwb | ||
| vfio | ||
| vhost | ||
| video | ||
| virt | ||
| virtio | ||
| vlynq | ||
| vme | ||
| w1 | ||
| watchdog | ||
| xen | ||
| zorro | ||
| Kconfig | ||
| Makefile | ||