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Subject[PATCH 2/3] opp: Allocate the OPP table outside of opp_table_lock
Date
There is no critical section which needs protection with locks while
allocating an OPP table, except while adding it to the opp_tables list.
And taking the opp_table_lock for the entire duration causes circular
dependency issues like the one mentioned below. This patch takes
another approach to reduce the size of the critical section to avoid
such issues, the details of that are present within the patch.

======================================================
WARNING: possible circular locking dependency detected
5.4.72 #14 Not tainted
------------------------------------------------------
chrome/1865 is trying to acquire lock:
ffffffdd34921750 (opp_table_lock){+.+.}, at: _find_opp_table+0x34/0x74

but task is already holding lock:
ffffff81f0fc71a8 (reservation_ww_class_mutex){+.+.}, at: submit_lock_objects+0x70/0x1ec

fscrypt: AES-256-CTS-CBC using implementation "cts-cbc-aes-ce"
which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:
-> #4 (reservation_ww_class_mutex){+.+.}:
__mutex_lock_common+0xec/0xc0c
ww_mutex_lock_interruptible+0x5c/0xc4
msm_gem_fault+0x2c/0x124
__do_fault+0x40/0x16c
handle_mm_fault+0x7cc/0xd98
do_page_fault+0x230/0x3b4
do_translation_fault+0x5c/0x78
do_mem_abort+0x4c/0xb4
el0_da+0x1c/0x20
-> #3 (&mm->mmap_sem){++++}:
__might_fault+0x70/0x98
compat_filldir+0xf8/0x48c
dcache_readdir+0x70/0x1dc
iterate_dir+0xd4/0x180
__arm64_compat_sys_getdents+0xa0/0x19c
el0_svc_common+0xa8/0x178
el0_svc_compat_handler+0x2c/0x40
el0_svc_compat+0x8/0x10
-> #2 (&sb->s_type->i_mutex_key#3){++++}:
down_write+0x54/0x16c
start_creating+0x68/0x128
debugfs_create_dir+0x28/0x114
opp_debug_register+0x8c/0xc0
_add_opp_dev_unlocked+0x5c/0x70
_add_opp_dev+0x38/0x58
_opp_get_opp_table+0xdc/0x1ac
dev_pm_opp_get_opp_table_indexed+0x24/0x30
dev_pm_opp_of_add_table_indexed+0x48/0x84
of_genpd_add_provider_onecell+0xc0/0x1b8
rpmhpd_probe+0x240/0x268
platform_drv_probe+0x90/0xb0
really_probe+0x134/0x2ec
driver_probe_device+0x64/0xfc
__device_attach_driver+0x8c/0xa4
bus_for_each_drv+0x90/0xd8
__device_attach+0xc0/0x148
device_initial_probe+0x20/0x2c
bus_probe_device+0x34/0x94
device_add+0x1fc/0x3b0
of_device_add+0x3c/0x4c
of_platform_device_create_pdata+0xb8/0xfc
of_platform_bus_create+0x1e4/0x368
of_platform_populate+0x70/0xbc
devm_of_platform_populate+0x58/0xa0
rpmh_rsc_probe+0x36c/0x3cc
platform_drv_probe+0x90/0xb0
really_probe+0x134/0x2ec
driver_probe_device+0x64/0xfc
__device_attach_driver+0x8c/0xa4
bus_for_each_drv+0x90/0xd8
__device_attach+0xc0/0x148
device_initial_probe+0x20/0x2c
bus_probe_device+0x34/0x94
device_add+0x1fc/0x3b0
of_device_add+0x3c/0x4c
of_platform_device_create_pdata+0xb8/0xfc
of_platform_bus_create+0x1e4/0x368
of_platform_bus_create+0x230/0x368
of_platform_populate+0x70/0xbc
of_platform_default_populate_init+0xa8/0xc0
do_one_initcall+0x1c8/0x3fc
do_initcall_level+0xb4/0x10c
do_basic_setup+0x30/0x48
kernel_init_freeable+0x124/0x1a4
kernel_init+0x14/0x104
ret_from_fork+0x10/0x18
-> #1 (&opp_table->lock){+.+.}:
__mutex_lock_common+0xec/0xc0c
mutex_lock_nested+0x40/0x50
_add_opp_dev+0x2c/0x58
_opp_get_opp_table+0xdc/0x1ac
dev_pm_opp_get_opp_table_indexed+0x24/0x30
dev_pm_opp_of_add_table_indexed+0x48/0x84
of_genpd_add_provider_onecell+0xc0/0x1b8
rpmhpd_probe+0x240/0x268
platform_drv_probe+0x90/0xb0
really_probe+0x134/0x2ec
driver_probe_device+0x64/0xfc
__device_attach_driver+0x8c/0xa4
bus_for_each_drv+0x90/0xd8
__device_attach+0xc0/0x148
device_initial_probe+0x20/0x2c
bus_probe_device+0x34/0x94
device_add+0x1fc/0x3b0
of_device_add+0x3c/0x4c
of_platform_device_create_pdata+0xb8/0xfc
of_platform_bus_create+0x1e4/0x368
of_platform_populate+0x70/0xbc
devm_of_platform_populate+0x58/0xa0
rpmh_rsc_probe+0x36c/0x3cc
platform_drv_probe+0x90/0xb0
really_probe+0x134/0x2ec
driver_probe_device+0x64/0xfc
__device_attach_driver+0x8c/0xa4
bus_for_each_drv+0x90/0xd8
__device_attach+0xc0/0x148
device_initial_probe+0x20/0x2c
bus_probe_device+0x34/0x94
device_add+0x1fc/0x3b0
of_device_add+0x3c/0x4c
of_platform_device_create_pdata+0xb8/0xfc
of_platform_bus_create+0x1e4/0x368
of_platform_populate+0x70/0xbc
devm_of_platform_populate+0x58/0xa0
rpmh_rsc_probe+0x36c/0x3cc
platform_drv_probe+0x90/0xb0
really_probe+0x134/0x2ec
driver_probe_device+0x64/0xfc
__device_attach_driver+0x8c/0xa4
bus_for_each_drv+0x90/0xd8
__device_attach+0xc0/0x148
device_initial_probe+0x20/0x2c
bus_probe_device+0x34/0x94
device_add+0x1fc/0x3b0
of_device_add+0x3c/0x4c
of_platform_device_create_pdata+0xb8/0xfc
of_platform_bus_create+0x1e4/0x368
of_platform_bus_create+0x230/0x368
of_platform_populate+0x70/0xbc
of_platform_default_populate_init+0xa8/0xc0
do_one_initcall+0x1c8/0x3fc
do_initcall_level+0xb4/0x10c
do_basic_setup+0x30/0x48
kernel_init_freeable+0x124/0x1a4
kernel_init+0x14/0x104
ret_from_fork+0x10/0x18
-> #0 (opp_table_lock){+.+.}:
__lock_acquire+0xee4/0x2450
lock_acquire+0x1cc/0x210
__mutex_lock_common+0xec/0xc0c
mutex_lock_nested+0x40/0x50
_find_opp_table+0x34/0x74
dev_pm_opp_find_freq_exact+0x2c/0xdc
a6xx_gmu_resume+0xc8/0xecc
a6xx_pm_resume+0x148/0x200
adreno_resume+0x28/0x34
pm_generic_runtime_resume+0x34/0x48
__rpm_callback+0x70/0x10c
rpm_callback+0x34/0x8c
rpm_resume+0x414/0x550
__pm_runtime_resume+0x7c/0xa0
msm_gpu_submit+0x60/0x1c0
msm_ioctl_gem_submit+0xadc/0xb60
drm_ioctl_kernel+0x9c/0x118
drm_ioctl+0x27c/0x408
drm_compat_ioctl+0xcc/0xdc
__se_compat_sys_ioctl+0x100/0x206c
__arm64_compat_sys_ioctl+0x20/0x2c
el0_svc_common+0xa8/0x178
el0_svc_compat_handler+0x2c/0x40
el0_svc_compat+0x8/0x10
other info that might help us debug this:
Chain exists of: opp_table_lock --> &mm->mmap_sem --> reservation_ww_class_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(reservation_ww_class_mutex);
lock(&mm->mmap_sem);
lock(reservation_ww_class_mutex);
lock(opp_table_lock);

*** DEADLOCK ***

3 locks held by chrome/1865:
#0: ffffff81edecc0d8 (&dev->struct_mutex){+.+.}, at: msm_ioctl_gem_submit+0x264/0xb60
#1: ffffff81d0000870 (reservation_ww_class_acquire){+.+.}, at: msm_ioctl_gem_submit+0x8e8/0xb60
#2: ffffff81f0fc71a8 (reservation_ww_class_mutex){+.+.}, at: submit_lock_objects+0x70/0x1ec
stack backtrace:
CPU: 0 PID: 1865 Comm: chrome Not tainted 5.4.72 #14
Hardware name: Google Lazor (rev1+) with LTE (DT)
Call trace:
dump_backtrace+0x0/0x158
show_stack+0x20/0x2c
dump_stack+0xc8/0x160
print_circular_bug+0x2c4/0x2c8
check_noncircular+0x1a8/0x1b0
__lock_acquire+0xee4/0x2450
lock_acquire+0x1cc/0x210
__mutex_lock_common+0xec/0xc0c
mutex_lock_nested+0x40/0x50
_find_opp_table+0x34/0x74
dev_pm_opp_find_freq_exact+0x2c/0xdc
a6xx_gmu_resume+0xc8/0xecc
a6xx_pm_resume+0x148/0x200
adreno_resume+0x28/0x34
pm_generic_runtime_resume+0x34/0x48
__rpm_callback+0x70/0x10c
rpm_callback+0x34/0x8c
rpm_resume+0x414/0x550
__pm_runtime_resume+0x7c/0xa0
msm_gpu_submit+0x60/0x1c0
msm_ioctl_gem_submit+0xadc/0xb60
drm_ioctl_kernel+0x9c/0x118
drm_ioctl+0x27c/0x408
drm_compat_ioctl+0xcc/0xdc
__se_compat_sys_ioctl+0x100/0x206c
__arm64_compat_sys_ioctl+0x20/0x2c
el0_svc_common+0xa8/0x178
el0_svc_compat_handler+0x2c/0x40
el0_svc_compat+0x8/0x10

Reported-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
drivers/opp/core.c | 47 +++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 84035ab8bb31..6f4a73a6391f 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -29,6 +29,8 @@
LIST_HEAD(opp_tables);
/* Lock to allow exclusive modification to the device and opp lists */
DEFINE_MUTEX(opp_table_lock);
+/* Flag indicating that opp_tables list is being updated at the moment */
+static bool opp_tables_busy;

static struct opp_device *_find_opp_dev(const struct device *dev,
struct opp_table *opp_table)
@@ -1111,8 +1113,6 @@ static struct opp_table *_allocate_opp_table(struct device *dev, int index)
INIT_LIST_HEAD(&opp_table->opp_list);
kref_init(&opp_table->kref);

- /* Secure the device table modification */
- list_add(&opp_table->node, &opp_tables);
return opp_table;

err:
@@ -1125,27 +1125,64 @@ void _get_opp_table_kref(struct opp_table *opp_table)
kref_get(&opp_table->kref);
}

+/*
+ * We need to make sure that the OPP table for a device doesn't get added twice,
+ * if this routine gets called in parallel with the same device pointer.
+ *
+ * The simplest way to enforce that is to perform everything (find existing
+ * table and if not found, create a new one) under the opp_table_lock, so only
+ * one creator gets access to the same. But that expands the critical section
+ * under the lock and may end up causing circular dependencies with frameworks
+ * like debugfs, interconnect or clock framework as they may be direct or
+ * indirect users of OPP core.
+ *
+ * And for that reason we have to go for a bit tricky implementation here, which
+ * uses the opp_tables_busy flag to indicate if another creator is in the middle
+ * of adding an OPP table and others should wait for it to finish.
+ */
static struct opp_table *_opp_get_opp_table(struct device *dev, int index)
{
struct opp_table *opp_table;

- /* Hold our table modification lock here */
+again:
mutex_lock(&opp_table_lock);

opp_table = _find_opp_table_unlocked(dev);
if (!IS_ERR(opp_table))
goto unlock;

+ /*
+ * The opp_tables list or an OPP table's dev_list is getting updated by
+ * another user, wait for it to finish.
+ */
+ if (unlikely(opp_tables_busy)) {
+ mutex_unlock(&opp_table_lock);
+ cpu_relax();
+ goto again;
+ }
+
+ opp_tables_busy = true;
opp_table = _managed_opp(dev, index);
+
+ /* Drop the lock to reduce the size of critical section */
+ mutex_unlock(&opp_table_lock);
+
if (opp_table) {
if (!_add_opp_dev(dev, opp_table)) {
dev_pm_opp_put_opp_table(opp_table);
opp_table = ERR_PTR(-ENOMEM);
}
- goto unlock;
+
+ mutex_lock(&opp_table_lock);
+ } else {
+ opp_table = _allocate_opp_table(dev, index);
+
+ mutex_lock(&opp_table_lock);
+ if (!IS_ERR(opp_table))
+ list_add(&opp_table->node, &opp_tables);
}

- opp_table = _allocate_opp_table(dev, index);
+ opp_tables_busy = false;

unlock:
mutex_unlock(&opp_table_lock);
--
2.25.0.rc1.19.g042ed3e048af
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