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71b2187714
In i915 hwmon sysfs getter path we now take a hwmon_lock, then acquire an
rpm wakeref. That results in lock inversion:
<4> [197.079335] ======================================================
<4> [197.085473] WARNING: possible circular locking dependency detected
<4> [197.091611] 6.8.0-rc7-Patchwork_129026v7-gc4dc92fb1152+ #1 Not tainted
<4> [197.098096] ------------------------------------------------------
<4> [197.104231] prometheus-node/839 is trying to acquire lock:
<4> [197.109680] ffffffff82764d80 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc+0x9a/0x350
<4> [197.116939]
but task is already holding lock:
<4> [197.122730] ffff88811b772a40 (&hwmon->hwmon_lock){+.+.}-{3:3}, at: hwm_energy+0x4b/0x100 [i915]
<4> [197.131543]
which lock already depends on the new lock.
...
<4> [197.507922] Chain exists of:
fs_reclaim --> >->reset.mutex --> &hwmon->hwmon_lock
<4> [197.518528] Possible unsafe locking scenario:
<4> [197.524411] CPU0 CPU1
<4> [197.528916] ---- ----
<4> [197.533418] lock(&hwmon->hwmon_lock);
<4> [197.537237] lock(>->reset.mutex);
<4> [197.543376] lock(&hwmon->hwmon_lock);
<4> [197.549682] lock(fs_reclaim);
...
<4> [197.632548] Call Trace:
<4> [197.634990] <TASK>
<4> [197.637088] dump_stack_lvl+0x64/0xb0
<4> [197.640738] check_noncircular+0x15e/0x180
<4> [197.652968] check_prev_add+0xe9/0xce0
<4> [197.656705] __lock_acquire+0x179f/0x2300
<4> [197.660694] lock_acquire+0xd8/0x2d0
<4> [197.673009] fs_reclaim_acquire+0xa1/0xd0
<4> [197.680478] __kmalloc+0x9a/0x350
<4> [197.689063] acpi_ns_internalize_name.part.0+0x4a/0xb0
<4> [197.694170] acpi_ns_get_node_unlocked+0x60/0xf0
<4> [197.720608] acpi_ns_get_node+0x3b/0x60
<4> [197.724428] acpi_get_handle+0x57/0xb0
<4> [197.728164] acpi_has_method+0x20/0x50
<4> [197.731896] acpi_pci_set_power_state+0x43/0x120
<4> [197.736485] pci_power_up+0x24/0x1c0
<4> [197.740047] pci_pm_default_resume_early+0x9/0x30
<4> [197.744725] pci_pm_runtime_resume+0x2d/0x90
<4> [197.753911] __rpm_callback+0x3c/0x110
<4> [197.762586] rpm_callback+0x58/0x70
<4> [197.766064] rpm_resume+0x51e/0x730
<4> [197.769542] rpm_resume+0x267/0x730
<4> [197.773020] rpm_resume+0x267/0x730
<4> [197.776498] rpm_resume+0x267/0x730
<4> [197.779974] __pm_runtime_resume+0x49/0x90
<4> [197.784055] __intel_runtime_pm_get+0x19/0xa0 [i915]
<4> [197.789070] hwm_energy+0x55/0x100 [i915]
<4> [197.793183] hwm_read+0x9a/0x310 [i915]
<4> [197.797124] hwmon_attr_show+0x36/0x120
<4> [197.800946] dev_attr_show+0x15/0x60
<4> [197.804509] sysfs_kf_seq_show+0xb5/0x100
Acquire the wakeref before the lock and hold it as long as the lock is
also held. Follow that pattern across the whole source file where similar
lock inversion can happen.
v2: Keep hardware read under the lock so the whole operation of updating
energy from hardware is still atomic (Guenter),
- instead, acquire the rpm wakeref before the lock and hold it as long
as the lock is held,
- use the same aproach for other similar places across the i915_hwmon.c
source file (Rodrigo).
Fixes:
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