100% CPU use with many torrents announcing to a tracker with an expired certificate

[ivan]

qBittorrent & operating system versions

qBittorrent: 4.3.8 x64
Operating system: NixOS 21.11-pre, NixOS 21.05
Qt: 5.15.2
libtorrent-rasterbar: 2.0.3, 2.0.4, or arvidn/libtorrent@69cb589

Specifically, I confirmed this issue and saw the same behavior with:

• (x86_64 NixOS) qbittorrent 4.3.8 with libtorrent arvidn/libtorrent@69cb589
• (x86_64 NixOS) qbittorrent 4.3.8 with libtorrent 2.0.4
• (x86_64 NixOS) qbittorrent 4.3.5 with libtorrent 2.0.3

What is the problem?

qBittorrent/libtorrent seems to use 100% CPU (one core) when it has many torrents announcing to a tracker with an expired HTTPS certificate.

There isn't really any visible indication or logging that indicates the problem, I just lucked into figuring it out.

Steps to reproduce

1. Try to download a few hundred torrents pointing to an https:// tracker with an expired certificate
2. Make sure 'Validate HTTP tracker certificates' is enabled (the default)
3. Observe 100% CPU use of one core, never decreasing, and strace showing one of the qbittorrent threads spinning fast on epoll_wait(15, [], 128, 0) = 0
4. Disable 'Validate HTTP tracker certificates'
5. Wait a few minutes and observe low CPU use
6. Repeat to confirm if desired (enable validation, force reannounce), it should always reproduce

Additional context

with 'Validate HTTP tracker certificates':

without 'Validate HTTP tracker certificates':

Log(s) & preferences file(s)

No response

[Chocobo1]

Nice find! you should also report this problem upstream: https://github.com/arvidn/libtorrent/issues

[ghost]

@arvidn

[ghost]

I could not reproduce it. I tested with 1000 torrents with 7-8 trackers that had expired certificates.
Tested on windows 10 x64 with qbt 4.4.3.1, libtorrent 2.0.6 and 1.2.16.
OpenSSL: 1.1.1o

[arvidn]

there was an issue related to HTTP tracker DNS lookups that, if they took too long, could trigger a 100% CPU busy loop. It was fixed in the recently released libtorrent 1.2.17 and 2.0.7

[ghost]

I’m not sure if they’re the same issue but this ticket indicates that turning off https tracker validation fixed it for OP.