Hello, On 2016-01-19 16:25, Ulf Hansson wrote:
+linux-pm, Daniel Kurtz, Nicolas Boichat On 4 January 2016 at 11:39, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote:During genpd_poweron, genpd->lock is acquired recursively for each parent (master) domain, which are separate obejcts. This confuses lockdep, which considers every operation on genpd->lock as being done on the same lock class. This leads to the following false positive warning: ============================================= [ INFO: possible recursive locking detected ] 4.4.0-rc4-xu3s #32 Not tainted --------------------------------------------- swapper/0/1 is trying to acquire lock: (&genpd->lock){+.+...}, at: [<c0361550>] __genpd_poweron+0x64/0x108 but task is already holding lock: (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&genpd->lock); lock(&genpd->lock); *** DEADLOCK *** May be due to missing lock nesting notation 3 locks held by swapper/0/1: #0: (&dev->mutex){......}, at: [<c0350910>] __driver_attach+0x48/0x98 #1: (&dev->mutex){......}, at: [<c0350920>] __driver_attach+0x58/0x98 #2: (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8 stack backtrace: CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4-xu3s #32 Hardware name: SAMSUNG EXYNOS (Flattened Device Tree) [<c0016c98>] (unwind_backtrace) from [<c00139c4>] (show_stack+0x10/0x14) [<c00139c4>] (show_stack) from [<c0270df0>] (dump_stack+0x84/0xc4) [<c0270df0>] (dump_stack) from [<c00780b8>] (__lock_acquire+0x1f88/0x215c) [<c00780b8>] (__lock_acquire) from [<c007886c>] (lock_acquire+0xa4/0xd0) [<c007886c>] (lock_acquire) from [<c0641f2c>] (mutex_lock_nested+0x70/0x4d4) [<c0641f2c>] (mutex_lock_nested) from [<c0361550>] (__genpd_poweron+0x64/0x108) [<c0361550>] (__genpd_poweron) from [<c0361b00>] (genpd_dev_pm_attach+0x170/0x1b8) [<c0361b00>] (genpd_dev_pm_attach) from [<c03520a8>] (platform_drv_probe+0x2c/0xac) [<c03520a8>] (platform_drv_probe) from [<c03507d4>] (driver_probe_device+0x208/0x2fc) [<c03507d4>] (driver_probe_device) from [<c035095c>] (__driver_attach+0x94/0x98) [<c035095c>] (__driver_attach) from [<c034ec14>] (bus_for_each_dev+0x68/0x9c) [<c034ec14>] (bus_for_each_dev) from [<c034fec8>] (bus_add_driver+0x1a0/0x218) [<c034fec8>] (bus_add_driver) from [<c035115c>] (driver_register+0x78/0xf8) [<c035115c>] (driver_register) from [<c0338488>] (exynos_drm_register_drivers+0x28/0x74) [<c0338488>] (exynos_drm_register_drivers) from [<c0338594>] (exynos_drm_init+0x6c/0xc4) [<c0338594>] (exynos_drm_init) from [<c00097f4>] (do_one_initcall+0x90/0x1dc) [<c00097f4>] (do_one_initcall) from [<c0895e08>] (kernel_init_freeable+0x158/0x1f8) [<c0895e08>] (kernel_init_freeable) from [<c063ecac>] (kernel_init+0x8/0xe8) [<c063ecac>] (kernel_init) from [<c000f7d0>] (ret_from_fork+0x14/0x24) This patch replaces mutex_lock with mutex_lock_nested() and uses recursion depth to annotate each genpd->lock operation with separate lockdep subclass. Reported-by: Anand Moon <linux.amoon@xxxxxxxxx> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>Thanks for looking into this! Daniel Kurtz, did also run into this issue [1] and reported it a while ago. There where some discussions and Daniel also posted a patch trying to solve the issue [2]. That approach didn't work out, and unfortunate I haven't yet been able to look closer into the issue. Sorry about that!--- drivers/base/power/domain.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c index b803790..e02ddf6 100644 --- a/drivers/base/power/domain.c +++ b/drivers/base/power/domain.c @@ -170,16 +170,15 @@ static void genpd_queue_power_off_work(struct generic_pm_domain *genpd) queue_work(pm_wq, &genpd->power_off_work); } -static int genpd_poweron(struct generic_pm_domain *genpd); - /** * __genpd_poweron - Restore power to a given PM domain and its masters. * @genpd: PM domain to power up. + * @depth: nesting count for lockdep. * * Restore power to @genpd and all of its masters so that it is possible to * resume a device belonging to it. */ -static int __genpd_poweron(struct generic_pm_domain *genpd) +static int __genpd_poweron(struct generic_pm_domain *genpd, unsigned int depth) { struct gpd_link *link; int ret = 0; @@ -194,11 +193,16 @@ static int __genpd_poweron(struct generic_pm_domain *genpd) * with it. */ list_for_each_entry(link, &genpd->slave_links, slave_node) { - genpd_sd_counter_inc(link->master); + struct generic_pm_domain *master = link->master; + + genpd_sd_counter_inc(master); + + mutex_lock_nested(&master->lock, depth + 1);Nested locks isn't a solution to a problem, but instead this tricks lockdep about what goes on. Right?
The only difference between mutex_lock_nested and mutex_lock is the way it is interpreted by deplock. The additional argument is deplock subclass of the lock. The name of this function is imho a bit misleading.
I am wondering whether there's another option available which better can instruct lockdep to not treat this as an error.
Similar solution is already applied in regulators and i2c cores, see regulator_lock_supply() and i2c_del_adapter() functions.
+ ret = __genpd_poweron(master, depth + 1); + mutex_unlock(&master->lock); - ret = genpd_poweron(link->master); if (ret) { - genpd_sd_counter_dec(link->master); + genpd_sd_counter_dec(master); goto err; } } @@ -230,11 +234,12 @@ static int genpd_poweron(struct generic_pm_domain *genpd) int ret; mutex_lock(&genpd->lock); - ret = __genpd_poweron(genpd); + ret = __genpd_poweron(genpd, 0); mutex_unlock(&genpd->lock); return ret; } + static int genpd_save_dev(struct generic_pm_domain *genpd, struct device *dev) { return GENPD_DEV_CALLBACK(genpd, int, save_state, dev); @@ -482,7 +487,7 @@ static int pm_genpd_runtime_resume(struct device *dev) } mutex_lock(&genpd->lock); - ret = __genpd_poweron(genpd); + ret = __genpd_poweron(genpd, 0); mutex_unlock(&genpd->lock); if (ret) -- 1.9.2Kind regards Uffe [1] http://www.spinics.net/lists/arm-kernel/msg471025.html [2] http://www.spinics.net/lists/stable/msg113650.html
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
