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When users try to remove PMU modules during perf sampling, kernel panic will happen because the pmu->read() is a NULL pointer here. INFO on HiSilicon hip08 platform as follow: pc : hisi_uncore_pmu_event_update+0x30/0xa4 [hisi_uncore_pmu] lr : hisi_uncore_pmu_read+0x20/0x2c [hisi_uncore_pmu] sp : ffff800010103e90 x29: ffff800010103e90 x28: ffff0027db0c0e40 x27: ffffa29a76f129d8 x26: ffffa29a77ceb000 x25: ffffa29a773a5000 x24: ffffa29a77392000 x23: ffffddffe5943f08 x22: ffff002784285960 x21: ffff002784285800 x20: ffff0027d2e76c80 x19: ffff0027842859e0 x18: ffff80003498bcc8 x17: ffffa29a76afe910 x16: ffffa29a7583f530 x15: 16151a1512061a1e x14: 0000000000000000 x13: ffffa29a76f1e238 x12: 0000000000000001 x11: 0000000000000400 x10: 00000000000009f0 x9 : ffff8000107b3e70 x8 : ffff0027db0c1890 x7 : ffffa29a773a7000 x6 : 00000007f5131013 x5 : 00000007f5131013 x4 : 09f257d417c00000 x3 : 00000002187bd7ce x2 : ffffa29a38f0f0d8 x1 : ffffa29a38eae268 x0 : ffff0027d2e76c80 Call trace: hisi_uncore_pmu_event_update+0x30/0xa4 [hisi_uncore_pmu] hisi_uncore_pmu_read+0x20/0x2c [hisi_uncore_pmu] __perf_event_read+0x1a0/0x1f8 flush_smp_call_function_queue+0xa0/0x160 generic_smp_call_function_single_interrupt+0x18/0x20 handle_IPI+0x31c/0x4dc gic_handle_irq+0x2c8/0x310 el1_irq+0xcc/0x180 arch_cpu_idle+0x4c/0x20c default_idle_call+0x20/0x30 do_idle+0x1b4/0x270 cpu_startup_entry+0x28/0x30 secondary_start_kernel+0x1a4/0x1fc To solve the above issue, current module should be registered to kernel, so that try_module_get() can be invoked when perf sampling starts. This adds the reference counting of module and could prevent users from removing modules during sampling. Reported-by: Haifeng Wang <wang.wanghaifeng@huawei.com> Signed-off-by: Qi Liu <liuqi115@huawei.com> Reviewed-by: John Garry <john.garry@huawei.com> Link: https://lore.kernel.org/r/1594891165-8228-1-git-send-email-liuqi115@huawei.com Signed-off-by: Will Deacon <will@kernel.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.