On Saturday, August 1, 2020 1:25:22 AM CEST Francisco Jerez wrote:
> kernel test robot <rong.a.chen@xxxxxxxxx> writes:
>
> > Greeting,
> >
> > FYI, we noticed the following commit (built with gcc-9):
> >
> > commit: 48fc4efcdd584e8f04da8b195262ec38221bd6db ("[PATCH v2 2/2] cpufreq: intel_pstate: Implement passive mode with HWP enabled")
> > url: https://github.com/0day-ci/linux/commits/Rafael-J-Wysocki/cpufreq-intel_pstate-Implement-passive-mode-with-HWP-enabled/20200717-014718
> > base: https://git.kernel.org/cgit/linux/kernel/git/rafael/linux-pm.git linux-next
> >
> > in testcase: kernel-selftests
> > with following parameters:
> >
> > group: kselftests-cpufreq
> > ucode: 0x5002f01
> >
> > test-description: The kernel contains a set of "self tests" under the tools/testing/selftests/ directory. These are intended to be small unit tests to exercise individual code paths in the kernel.
> > test-url: https://www.kernel.org/doc/Documentation/kselftest.txt
> >
> >
> > on test machine: 192 threads Intel(R) Xeon(R) Platinum 9242 CPU @ 2.30GHz with 192G memory
> >
> > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> >
> >
> >
> >
> > If you fix the issue, kindly add following tag
> > Reported-by: kernel test robot <rong.a.chen@xxxxxxxxx>
> >
> >
> > [ 74.745395] WARNING: possible circular locking dependency detected
> > [ 74.752071] 5.8.0-rc5-00064-g48fc4efcdd584 #1 Not tainted
> > [ 74.757949] ------------------------------------------------------
> > [ 74.764604] main.sh/3019 is trying to acquire lock:
> > [ 74.769954] ffffffff82ec7f08 (intel_pstate_driver_lock){+.+.}-{3:3}, at: store_energy_performance_preference+0xec/0x250
> > [ 74.781228]
> > [ 74.781228] but task is already holding lock:
> > [ 74.788017] ffff88b07b5f8380 (&policy->rwsem){++++}-{3:3}, at: store+0x69/0xa0
> > [ 74.795711]
> > [ 74.795711] which lock already depends on the new lock.
> > [ 74.795711]
> > [ 74.805222]
> > [ 74.805222] the existing dependency chain (in reverse order) is:
> > [ 74.813529]
> > [ 74.813529] -> #2 (&policy->rwsem){++++}-{3:3}:
> > [ 74.820371] __lock_acquire+0x538/0xa90
> > [ 74.825144] lock_acquire+0xab/0x390
> > [ 74.829660] down_write+0x38/0x70
> > [ 74.833910] store+0x69/0xa0
> > [ 74.837724] kernfs_fop_write+0xdc/0x1c0
> > [ 74.842576] vfs_write+0xee/0x220
> > [ 74.846814] ksys_write+0x68/0xe0
> > [ 74.851039] do_syscall_64+0x52/0xb0
> > [ 74.855512] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [ 74.861463]
> > [ 74.861463] -> #1 (cpu_hotplug_lock){++++}-{0:0}:
> > [ 74.868395] __lock_acquire+0x538/0xa90
> > [ 74.873127] lock_acquire+0xab/0x390
> > [ 74.877597] cpus_read_lock+0x39/0xd0
> > [ 74.882146] cpufreq_register_driver+0xb6/0x2a0
> > [ 74.887556] intel_pstate_register_driver+0x32/0x70
> > [ 74.893312] intel_pstate_init+0x45d/0x4ca
> > [ 74.898281] do_one_initcall+0x5d/0x330
> > [ 74.902984] kernel_init_freeable+0x248/0x2c9
> > [ 74.908185] kernel_init+0xa/0x112
> > [ 74.912430] ret_from_fork+0x1f/0x30
> > [ 74.916850]
> > [ 74.916850] -> #0 (intel_pstate_driver_lock){+.+.}-{3:3}:
> > [ 74.924376] check_prev_add+0x8e/0x9f0
> > [ 74.928988] validate_chain+0x79b/0x1080
> > [ 74.933773] __lock_acquire+0x538/0xa90
> > [ 74.938469] lock_acquire+0xab/0x390
> > [ 74.942896] __mutex_lock+0xac/0x9c0
> > [ 74.947318] store_energy_performance_preference+0xec/0x250
> > [ 74.953735] store+0x7c/0xa0
> > [ 74.957458] kernfs_fop_write+0xdc/0x1c0
> > [ 74.962231] vfs_write+0xee/0x220
> > [ 74.966395] ksys_write+0x68/0xe0
> > [ 74.970549] do_syscall_64+0x52/0xb0
> > [ 74.974975] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [ 74.980859]
> > [ 74.980859] other info that might help us debug this:
> > [ 74.980859]
> > [ 74.989744] Chain exists of:
> > [ 74.989744] intel_pstate_driver_lock --> cpu_hotplug_lock --> &policy->rwsem
> > [ 74.989744]
> > [ 75.002149] Possible unsafe locking scenario:
> > [ 75.002149]
> > [ 75.008643] CPU0 CPU1
> > [ 75.013461] ---- ----
> > [ 75.018275] lock(&policy->rwsem);
> > [ 75.022037] lock(cpu_hotplug_lock);
> > [ 75.028495] lock(&policy->rwsem);
> > [ 75.034773] lock(intel_pstate_driver_lock);
> > [ 75.039427]
> > [ 75.039427] *** DEADLOCK ***
> > [ 75.039427]
> > [ 75.046168] 5 locks held by main.sh/3019:
> > [ 75.050456] #0: ffff888b9d973438 (sb_writers#4){.+.+}-{0:0}, at: vfs_write+0x1ba/0x220
> > [ 75.058750] #1: ffff888beaaec488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write+0xa5/0x1c0
> > [ 75.067413] #2: ffff8898284de890 (kn->active#163){.+.+}-{0:0}, at: kernfs_fop_write+0xad/0x1c0
> > [ 75.076422] #3: ffffffff82c73a70 (cpu_hotplug_lock){++++}-{0:0}, at: store+0x26/0xa0
> > [ 75.084566] #4: ffff88b07b5f8380 (&policy->rwsem){++++}-{3:3}, at: store+0x69/0xa0
> > [ 75.092528]
> > [ 75.092528] stack backtrace:
> > [ 75.097500] CPU: 0 PID: 3019 Comm: main.sh Not tainted 5.8.0-rc5-00064-g48fc4efcdd584 #1
> > [ 75.105902] Hardware name: Intel Corporation ............/S9200WKBRD2, BIOS SE5C620.86B.0D.01.0552.060220191912 06/02/2019
> > [ 75.117274] Call Trace:
> > [ 75.120081] dump_stack+0x96/0xd0
> > [ 75.123754] check_noncircular+0x162/0x180
> > [ 75.128220] check_prev_add+0x8e/0x9f0
> > [ 75.132325] validate_chain+0x79b/0x1080
> > [ 75.136589] __lock_acquire+0x538/0xa90
> > [ 75.140767] lock_acquire+0xab/0x390
> > [ 75.144684] ? store_energy_performance_preference+0xec/0x250
> > [ 75.150775] __mutex_lock+0xac/0x9c0
> > [ 75.154697] ? store_energy_performance_preference+0xec/0x250
> > [ 75.160786] ? __lock_acquire+0x538/0xa90
> > [ 75.165147] ? store_energy_performance_preference+0xec/0x250
> > [ 75.171282] ? sscanf+0x4e/0x70
> > [ 75.174781] ? store_energy_performance_preference+0xec/0x250
> > [ 75.180886] store_energy_performance_preference+0xec/0x250
> > [ 75.186816] store+0x7c/0xa0
> > [ 75.190056] kernfs_fop_write+0xdc/0x1c0
> > [ 75.194338] vfs_write+0xee/0x220
> > [ 75.198011] ksys_write+0x68/0xe0
> > [ 75.201685] do_syscall_64+0x52/0xb0
> > [ 75.205617] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [ 75.211051] RIP: 0033:0x7f2c1dfa9504
> > [ 75.214999] Code: Bad RIP value.
> > [ 75.218582] RSP: 002b:00007fffe26da068 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> >
>
> Was about to review v4 of this series, but from my reading of it it
> seems like this locking inversion situation could also occur with your
> last revision. Is it a legitimate concern Rafael?
>
> >[...]
>
There a mistake in the patch.
Because energy_performance_preference is a policy attribute,
it is not valid to acquire intel_pstate_driver_lock in its "store"
routine, but that routine can check the driver pointer without additional
locking, because that pointer cannot change while it is running.
I've just sent a v5 to fix this problem.
Thanks!
