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c48fb3bbe9
We hold the read lock on CPU hotplug to simply copy the online mask, which is not really needed. And this can cause a lockdep warning, like : [ 54.632093] ====================================================== [ 54.638207] WARNING: possible circular locking dependency detected [ 54.644322] 4.18.0-rc3-00042-g2d39e6356bb7-dirty #309 Not tainted [ 54.650350] ------------------------------------------------------ [ 54.656464] perf/2862 is trying to acquire lock: [ 54.661031] 000000007e21d170 (&event->mmap_mutex){+.+.}, at: perf_event_set_output+0x98/0x138 [ 54.669486] [ 54.669486] but task is already holding lock: [ 54.675256] 000000001080eb1b (&cpuctx_mutex){+.+.}, at: perf_event_ctx_lock_nested+0xf8/0x1f0 [ 54.683704] [ 54.683704] which lock already depends on the new lock. [ 54.683704] [ 54.691797] [ 54.691797] the existing dependency chain (in reverse order) is: [ 54.699201] [ 54.699201] -> #3 (&cpuctx_mutex){+.+.}: [ 54.704556] __mutex_lock+0x70/0x808 [ 54.708608] mutex_lock_nested+0x1c/0x28 [ 54.713005] perf_event_init_cpu+0x8c/0xd8 [ 54.717574] perf_event_init+0x194/0x1d4 [ 54.721971] start_kernel+0x2b8/0x42c [ 54.726107] [ 54.726107] -> #2 (pmus_lock){+.+.}: [ 54.731114] __mutex_lock+0x70/0x808 [ 54.735165] mutex_lock_nested+0x1c/0x28 [ 54.739560] perf_event_init_cpu+0x30/0xd8 [ 54.744129] cpuhp_invoke_callback+0x84/0x248 [ 54.748954] _cpu_up+0xe8/0x1c8 [ 54.752576] do_cpu_up+0xa8/0xc8 [ 54.756283] cpu_up+0x10/0x18 [ 54.759731] smp_init+0xa0/0x114 [ 54.763438] kernel_init_freeable+0x120/0x288 [ 54.768264] kernel_init+0x10/0x108 [ 54.772230] ret_from_fork+0x10/0x18 [ 54.776279] [ 54.776279] -> #1 (cpu_hotplug_lock.rw_sem){++++}: [ 54.782492] cpus_read_lock+0x34/0xb0 [ 54.786631] etm_setup_aux+0x5c/0x308 [ 54.790769] rb_alloc_aux+0x1ec/0x300 [ 54.794906] perf_mmap+0x284/0x610 [ 54.798787] mmap_region+0x388/0x570 [ 54.802838] do_mmap+0x344/0x4f8 [ 54.806544] vm_mmap_pgoff+0xe4/0x110 [ 54.810682] ksys_mmap_pgoff+0xa8/0x240 [ 54.814992] sys_mmap+0x18/0x28 [ 54.818613] el0_svc_naked+0x30/0x34 [ 54.822661] [ 54.822661] -> #0 (&event->mmap_mutex){+.+.}: [ 54.828445] lock_acquire+0x48/0x68 [ 54.832409] __mutex_lock+0x70/0x808 [ 54.836459] mutex_lock_nested+0x1c/0x28 [ 54.840855] perf_event_set_output+0x98/0x138 [ 54.845680] _perf_ioctl+0x2a0/0x6a0 [ 54.849731] perf_ioctl+0x3c/0x68 [ 54.853526] do_vfs_ioctl+0xb8/0xa20 [ 54.857577] ksys_ioctl+0x80/0xb8 [ 54.861370] sys_ioctl+0xc/0x18 [ 54.864990] el0_svc_naked+0x30/0x34 [ 54.869039] [ 54.869039] other info that might help us debug this: [ 54.869039] [ 54.876960] Chain exists of: [ 54.876960] &event->mmap_mutex --> pmus_lock --> &cpuctx_mutex [ 54.876960] [ 54.887217] Possible unsafe locking scenario: [ 54.887217] [ 54.893073] CPU0 CPU1 [ 54.897552] ---- ---- [ 54.902030] lock(&cpuctx_mutex); [ 54.905396] lock(pmus_lock); [ 54.910911] lock(&cpuctx_mutex); [ 54.916770] lock(&event->mmap_mutex); [ 54.920566] [ 54.920566] *** DEADLOCK *** [ 54.920566] [ 54.926424] 1 lock held by perf/2862: [ 54.930042] #0: 000000001080eb1b (&cpuctx_mutex){+.+.}, at: perf_event_ctx_lock_nested+0xf8/0x1f0 Since we have per-cpu array for the paths, we simply don't care about the number of online CPUs. This patch gets rid of the {get/put}_online_cpus(). Reported-by: Mathieu Poirier <mathieu.poirier@linaro.org> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org> 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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.