Alexey Gladkov <gladkov.alexey@xxxxxxxxx> writes: > On Wed, Feb 24, 2021 at 12:50:21PM -0600, Eric W. Biederman wrote: >> Alexey Gladkov <gladkov.alexey@xxxxxxxxx> writes: >> >> > On Wed, Feb 24, 2021 at 10:54:17AM -0600, Eric W. Biederman wrote: >> >> kernel test robot <oliver.sang@xxxxxxxxx> writes: >> >> >> >> > Greeting, >> >> > >> >> > FYI, we noticed a -82.7% regression of stress-ng.sigsegv.ops_per_sec due to commit: >> >> > >> >> > >> >> > commit: d28296d2484fa11e94dff65e93eb25802a443d47 ("[PATCH v7 5/7] Reimplement RLIMIT_SIGPENDING on top of ucounts") >> >> > url: https://github.com/0day-ci/linux/commits/Alexey-Gladkov/Count-rlimits-in-each-user-namespace/20210222-175836 >> >> > base: https://git.kernel.org/cgit/linux/kernel/git/shuah/linux-kselftest.git next >> >> > >> >> > in testcase: stress-ng >> >> > on test machine: 48 threads Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz with 112G memory >> >> > with following parameters: >> >> > >> >> > nr_threads: 100% >> >> > disk: 1HDD >> >> > testtime: 60s >> >> > class: interrupt >> >> > test: sigsegv >> >> > cpufreq_governor: performance >> >> > ucode: 0x42e >> >> > >> >> > >> >> > In addition to that, the commit also has significant impact on the >> >> > following tests: >> >> >> >> Thank you. Now we have a sense of where we need to test the performance >> >> of these changes carefully. >> > >> > One of the reasons for this is that I rolled back the patch that changed >> > the ucounts.count type to atomic_t. Now get_ucounts() is forced to use a >> > spin_lock to increase the reference count. >> >> Which given the hickups with getting a working version seems justified. >> >> Now we can add incremental patches on top to improve the performance. > > I'm not sure that get_ucounts() should be used in __sigqueue_alloc() [1]. > I tried removing it and running KASAN tests that were failing before. So > far, I have not found any problems. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/legion/linux.git/tree/kernel/signal.c?h=patchset/per-userspace-rlimit/v7.1&id=2d4a2e2be7db42c95acb98abfc2a9b370ddd0604#n428 Hmm. The code you posted still seems to include the get_ucounts. I like the idea of not needing to increment and decrement the ucount reference count every time a signal is sent, unfortunately there is a problem. The way we have implemented setresuid allows different threads in a threaded application to have different cred->user values. That is actually an extension of what posix supports and pthreads will keep the creds of a process in sync. Still I recall looking into this a few years ago and there were a few applications that take advantage of the linux behavior. In principle I think it is possible to hold a ucount reference in somewhere such as task->signal. In practice there are enough complicating factors I don't immediately see how to implement that. If the creds were stored in signal_struct instead of in task_struct we could simply move the sigpending counts in set_user, when the uid of a process changed. With the current state I don't know how to pick which is the real user. Eric