RtlFindNextForwardRunClear holds NTFS lock for multiple seconds

[randomascii]

In some cases on some machines if system restore is enabled then RtlFindNextForwardRunClear may end up spinning in a seven-instruction loop for multiple seconds while holding a lock. This prevents basic operations like WriteFile from completing. In the case where this was first hit this caused a 64-processor machine to grind to a halt, repeatedly.

A full explanation can be found here:

https://randomascii.wordpress.com/2019/10/20/63-cores-blocked-by-seven-instructions/

I have heard that this bug has been fixed but was asked to file an issue to formally track it:
https://twitter.com/richturn_ms/status/1330947602129448961

[bitcrazed]

Thanks for filing here Bruce.

[bitcrazed]

Update: This bug has now been fixed internally and will work its way through our engineering system into a future OS release.

Summary of the fix:

Fixed perf bug in VspQueryCopyFreeBitmap.

Bruce Dawson on the Google Chrome team pointed out a bug where Chromium builds had several hiccups in I/O. Others have also hit the same bug.
The root cause is that the search for free regions of the volsnap CoW bitmap were incorrectly unbounded and could take multiple milliseconds on a 1TB drive.

Thanks for reporting this issue. Glad to have fixed it!

Will update this thread with details of which builds this fix will first arrive in.

[zjturner]

Any updates yet on what build this will be fixed in? We still regularly hit this issue when imaging new machines, so I'm assuming it's not live yet?

[AvriMSFT]

I've sent a note to the team and am waiting on a status update. I'll post here as soon as I get an answer

[klauroblox]

Any updates on when this will be out?

a year later, any update?

[Alois-xx]

When is this fixed? I have several incidents of this issue seen in the field and even one repro. When will this be backmerged to all still supported OS editions?

[AvriMSFT]

Hey folks! I just pinged the team for an update on this. Thanks for your patience and I'll post here as soon as I hear back.