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commit02d029a41dupstream. perf_init_event tries multiple init callbacks and does not reset the event state between tries. When x86_pmu_event_init runs, it unconditionally sets the destroy callback to hw_perf_event_destroy. On the next init attempt after x86_pmu_event_init, in perf_try_init_event, if the pmu's capabilities includes PERF_PMU_CAP_NO_EXCLUDE, the destroy callback will be run. However, if the next init didn't set the destroy callback, hw_perf_event_destroy will be run (since the callback wasn't reset). Looking at other pmu init functions, the common pattern is to only set the destroy callback on a successful init. Resetting the callback on failure tries to replicate that pattern. This was discovered after commitf11dd0d805("perf/x86/amd/ibs: Extend PERF_PMU_CAP_NO_EXCLUDE to IBS Op") when the second (and only second) run of the perf tool after a reboot results in 0 samples being generated. The extra run of hw_perf_event_destroy results in active_events having an extra decrement on each perf run. The second run has active_events == 0 and every subsequent run has active_events < 0. When active_events == 0, the NMI handler will early-out and not record any samples. Signed-off-by: Anand K Mistry <amistry@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210929170405.1.I078b98ee7727f9ae9d6df8262bad7e325e40faf0@changeid Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.