On 3/11/24 09:58, Rodrigo Vivi wrote:
On Mon, Mar 11, 2024 at 09:06:46AM +0100, Janusz Krzysztofik wrote:
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
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@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 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);
+
This is not enough.
check hwm_locked_with_pm_intel_uncore_rmw()
It looks like we need to rethink this lock entirely here.
I would have assumed that the lock was supposed to ensure that
reading the register value and the subsequent update of accum_energy
and reg_val_prev was synchronized. This is no longer the case
after this patch has been applied. Given that, I would agree that
it would make sense to define what the lock is supposed to protect
before changing its scope.
Guenter
