Fix bug #76003: FPM /status reports wrong number of active processe #8331
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Looks reasonable to me. |
The fix introduces early locking of scoreboard when it is updated which prevents the race condition causing an incorrect number of active processes being set.
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Just for the records, I have done extra testing of this with various number of max_children (5, 10, 64) with a bit more optimized configuration that can be seen here: https://github.com/bukka/php-util/blob/aa07dbe8075edfe8d03111bf81fc87654802403c/tests/fpm/status-wrong-active-procs/fpm.conf . I haven't noticed any perf regression that would be caused slightly longer lock that this PR introduces. Just to note this test executes really short requests so if there was any impact, it would be more visible here than for longer request. I'm quite happy with this and will be most likely merging it tomorrow. |
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Merged as 33bb201 |
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The fix introduces early locking of scoreboard when it is updated which prevents the race condition causing an incorrect number of active processes being set.
This is unfortunately not easily repeatable in the test environment so this was tested manually using following setup: https://github.com/bukka/php-util/tree/92a02d92914821bd194867360d563ed5a462a80f/tests/fpm/status-wrong-active-procs . It allows to load test FPM using wrk which triggers around 15k requests in 30s and then polls the status pages to check if the active process are above the set maximum of 5. This was quickly achievable before the fix (often 6 active processes were visible) but it no longer happens after this fix. The load test also didn't show any visible perf regression.