[PATCH] drm/i915/hwmon: Fix locking inversion in sysfs getter

[Janusz Krzysztofik]

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 --> &gt->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(&gt->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

However, the lock is only intended to protect either a hwmon overflow
counter or rmw hardware operations.  There is no need to hold the lock,
only the wakeref, while reading from hardware.

Acquire the lock after hardware read under rpm wakeref.

Fixes: c41b8bdcc297 ("drm/i915/hwmon: Show device level energy usage")
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at linux.intel.com>
Cc: <stable at vger.kernel.org> # v6.2+
---
 drivers/gpu/drm/i915/i915_hwmon.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_hwmon.c b/drivers/gpu/drm/i915/i915_hwmon.c
index 8c3f443c8347e..faf7670de6e06 100644
--- a/drivers/gpu/drm/i915/i915_hwmon.c
+++ b/drivers/gpu/drm/i915/i915_hwmon.c
@@ -136,11 +136,11 @@ hwm_energy(struct hwm_drvdata *ddat, long *energy)
 	else
 		rgaddr = hwmon->rg.energy_status_all;
 
-	mutex_lock(&hwmon->hwmon_lock);
-
 	with_intel_runtime_pm(uncore->rpm, wakeref)
 		reg_val = intel_uncore_read(uncore, rgaddr);
 
+	mutex_lock(&hwmon->hwmon_lock);
+
 	if (reg_val >= ei->reg_val_prev)
 		ei->accum_energy += reg_val - ei->reg_val_prev;
 	else
-- 
2.43.0