[PATCH 4.9 030/108] PM / runtime: Avoid false-positive warnings from might_sleep_if()

Greg Kroah-Hartman
2017-06-15T18:23:02Z

From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

[ Upstream commit a9306a63631493afc75893a4ac405d4e1cbae6aa ]

The might_sleep_if() assertions in __pm_runtime_idle(),
__pm_runtime_suspend() and __pm_runtime_resume() may generate
false-positive warnings in some situations. For example, that
happens if a nested pm_runtime_get_sync()/pm_runtime_put() pair
is executed with disabled interrupts within an outer
pm_runtime_get_sync()/pm_runtime_put() section for the same device.
[Generally, pm_runtime_get_sync() may sleep, so it should not be
called with disabled interrupts, but in this particular case the
previous pm_runtime_get_sync() guarantees that the device will not
be suspended, so the inner pm_runtime_get_sync() will return
immediately after incrementing the device's usage counter.]

That started to happen in the i915 driver in 4.10-rc, leading to
the following splat:

BUG: sleeping function called from invalid context at drivers/base/power/runtime.c:1032
in_atomic(): 1, irqs_disabled(): 0, pid: 1500, name: Xorg
1 lock held by Xorg/1500:
#0: (&dev->struct_mutex){+.+.+.}, at:
[<ffffffffa0680c13>] i915_mutex_lock_interruptible+0x43/0x140 [i915]
CPU: 0 PID: 1500 Comm: Xorg Not tainted
Call Trace:
dump_stack+0x85/0xc2
___might_sleep+0x196/0x260
__might_sleep+0x53/0xb0
__pm_runtime_resume+0x7a/0x90
intel_runtime_pm_get+0x25/0x90 [i915]
aliasing_gtt_bind_vma+0xaa/0xf0 [i915]
i915_vma_bind+0xaf/0x1e0 [i915]
i915_gem_execbuffer_relocate_entry+0x513/0x6f0 [i915]
i915_gem_execbuffer_relocate_vma.isra.34+0x188/0x250 [i915]
? trace_hardirqs_on+0xd/0x10
? i915_gem_execbuffer_reserve_vma.isra.31+0x152/0x1f0 [i915]
? i915_gem_execbuffer_reserve.isra.32+0x372/0x3a0 [i915]
i915_gem_do_execbuffer.isra.38+0xa70/0x1a40 [i915]
? __might_fault+0x4e/0xb0
i915_gem_execbuffer2+0xc5/0x260 [i915]
? __might_fault+0x4e/0xb0
drm_ioctl+0x206/0x450 [drm]
? i915_gem_execbuffer+0x340/0x340 [i915]
? __fget+0x5/0x200
do_vfs_ioctl+0x91/0x6f0
? __fget+0x111/0x200
? __fget+0x5/0x200
SyS_ioctl+0x79/0x90
entry_SYSCALL_64_fastpath+0x23/0xc6

even though the code triggering it is correct.

Unfortunately, the might_sleep_if() assertions in question are
too coarse-grained to cover such cases correctly, so make them
a bit less sensitive in order to avoid the false-positives.

Reported-and-tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/base/power/runtime.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -889,13 +889,13 @@ int __pm_runtime_idle(struct device *dev
unsigned long flags;
int retval;

- might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
-
if (rpmflags & RPM_GET_PUT) {
if (!atomic_dec_and_test(&dev->power.usage_count))
return 0;
}

+ might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
+
spin_lock_irqsave(&dev->power.lock, flags);
retval = rpm_idle(dev, rpmflags);
spin_unlock_irqrestore(&dev->power.lock, flags);
@@ -921,13 +921,13 @@ int __pm_runtime_suspend(struct device *
unsigned long flags;
int retval;

- might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
-
if (rpmflags & RPM_GET_PUT) {
if (!atomic_dec_and_test(&dev->power.usage_count))
return 0;
}

+ might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
+
spin_lock_irqsave(&dev->power.lock, flags);
retval = rpm_suspend(dev, rpmflags);
spin_unlock_irqrestore(&dev->power.lock, flags);
@@ -952,7 +952,8 @@ int __pm_runtime_resume(struct device *d
unsigned long flags;
int retval;

- might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
+ might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe &&
+ dev->power.runtime_status != RPM_ACTIVE);

if (rpmflags & RPM_GET_PUT)
atomic_inc(&dev->power.usage_count);