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SubjectRe: [PATCH v2] PM: domains: Shrink locking area of the gpd_list_lock
On Thu, 24 Jun 2021 at 22:18, Stephen Boyd <swboyd@chromium.org> wrote:
>
> On trogdor devices I see the following lockdep splat when stopping
> youtube with lockdep enabled in the kernel.
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.13.0-rc2 #71 Not tainted
> ------------------------------------------------------
> ThreadPoolSingl/3969 is trying to acquire lock:
> ffffff80d4d5c080 (&inst->lock#3){+.+.}-{3:3}, at: vdec_buf_cleanup+0x3c/0x17c [venus_dec]
>
> but task is already holding lock:
> ffffff80d3c3c4f8 (&q->mmap_lock){+.+.}-{3:3}, at: vb2_core_reqbufs+0xe4/0x390 [videobuf2_common]
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #5 (&q->mmap_lock){+.+.}-{3:3}:
> __mutex_lock_common+0xcc/0xb88
> mutex_lock_nested+0x5c/0x68
> vb2_mmap+0xf4/0x290 [videobuf2_common]
> v4l2_m2m_fop_mmap+0x44/0x50 [v4l2_mem2mem]
> v4l2_mmap+0x5c/0xa4
> mmap_region+0x310/0x5a4
> do_mmap+0x348/0x43c
> vm_mmap_pgoff+0xfc/0x178
> ksys_mmap_pgoff+0x84/0xfc
> __arm64_compat_sys_aarch32_mmap2+0x2c/0x38
> invoke_syscall+0x54/0x110
> el0_svc_common+0x88/0xf0
> do_el0_svc_compat+0x28/0x34
> el0_svc_compat+0x24/0x34
> el0_sync_compat_handler+0xc0/0xf0
> el0_sync_compat+0x19c/0x1c0
>
> -> #4 (&mm->mmap_lock){++++}-{3:3}:
> __might_fault+0x60/0x88
> filldir64+0x124/0x3a0
> dcache_readdir+0x7c/0x1ec
> iterate_dir+0xc4/0x184
> __arm64_sys_getdents64+0x78/0x170
> invoke_syscall+0x54/0x110
> el0_svc_common+0xa8/0xf0
> do_el0_svc_compat+0x28/0x34
> el0_svc_compat+0x24/0x34
> el0_sync_compat_handler+0xc0/0xf0
> el0_sync_compat+0x19c/0x1c0
>
> -> #3 (&sb->s_type->i_mutex_key#3){++++}-{3:3}:
> down_write+0x94/0x1f4
> start_creating+0xb0/0x174
> debugfs_create_dir+0x28/0x138
> opp_debug_register+0x88/0xc0
> _add_opp_dev+0x84/0x9c
> _add_opp_table_indexed+0x16c/0x310
> _of_add_table_indexed+0x70/0xb5c
> dev_pm_opp_of_add_table_indexed+0x20/0x2c
> of_genpd_add_provider_onecell+0xc4/0x1c8
> rpmhpd_probe+0x21c/0x278
> platform_probe+0xb4/0xd4
> really_probe+0x140/0x35c
> driver_probe_device+0x90/0xcc
> __device_attach_driver+0xa4/0xc0
> bus_for_each_drv+0x8c/0xd8
> __device_attach+0xc4/0x150
> device_initial_probe+0x20/0x2c
> bus_probe_device+0x40/0xa4
> device_add+0x22c/0x3fc
> of_device_add+0x44/0x54
> of_platform_device_create_pdata+0xb0/0xf4
> of_platform_bus_create+0x1d0/0x350
> of_platform_populate+0x80/0xd4
> devm_of_platform_populate+0x64/0xb0
> rpmh_rsc_probe+0x378/0x3dc
> platform_probe+0xb4/0xd4
> really_probe+0x140/0x35c
> driver_probe_device+0x90/0xcc
> __device_attach_driver+0xa4/0xc0
> bus_for_each_drv+0x8c/0xd8
> __device_attach+0xc4/0x150
> device_initial_probe+0x20/0x2c
> bus_probe_device+0x40/0xa4
> device_add+0x22c/0x3fc
> of_device_add+0x44/0x54
> of_platform_device_create_pdata+0xb0/0xf4
> of_platform_bus_create+0x1d0/0x350
> of_platform_bus_create+0x21c/0x350
> of_platform_populate+0x80/0xd4
> of_platform_default_populate_init+0xb8/0xd4
> do_one_initcall+0x1b4/0x400
> do_initcall_level+0xa8/0xc8
> do_initcalls+0x5c/0x9c
> do_basic_setup+0x2c/0x38
> kernel_init_freeable+0x1a4/0x1ec
> kernel_init+0x20/0x118
> ret_from_fork+0x10/0x30
>
> -> #2 (gpd_list_lock){+.+.}-{3:3}:
> __mutex_lock_common+0xcc/0xb88
> mutex_lock_nested+0x5c/0x68
> __genpd_dev_pm_attach+0x70/0x18c
> genpd_dev_pm_attach_by_id+0xe4/0x158
> genpd_dev_pm_attach_by_name+0x48/0x60
> dev_pm_domain_attach_by_name+0x2c/0x38
> dev_pm_opp_attach_genpd+0xac/0x160
> vcodec_domains_get+0x94/0x14c [venus_core]
> core_get_v4+0x150/0x188 [venus_core]
> venus_probe+0x138/0x444 [venus_core]
> platform_probe+0xb4/0xd4
> really_probe+0x140/0x35c
> driver_probe_device+0x90/0xcc
> device_driver_attach+0x58/0x7c
> __driver_attach+0xc8/0xe0
> bus_for_each_dev+0x88/0xd4
> driver_attach+0x30/0x3c
> bus_add_driver+0x10c/0x1e0
> driver_register+0x70/0x108
> __platform_driver_register+0x30/0x3c
> 0xffffffde113e1044
> do_one_initcall+0x1b4/0x400
> do_init_module+0x64/0x1fc
> load_module+0x17f4/0x1958
> __arm64_sys_finit_module+0xb4/0xf0
> invoke_syscall+0x54/0x110
> el0_svc_common+0x88/0xf0
> do_el0_svc_compat+0x28/0x34
> el0_svc_compat+0x24/0x34
> el0_sync_compat_handler+0xc0/0xf0
> el0_sync_compat+0x19c/0x1c0
>
> -> #1 (&opp_table->genpd_virt_dev_lock){+.+.}-{3:3}:
> __mutex_lock_common+0xcc/0xb88
> mutex_lock_nested+0x5c/0x68
> _set_required_opps+0x74/0x120
> _set_opp+0x94/0x37c
> dev_pm_opp_set_rate+0xa0/0x194
> core_clks_set_rate+0x28/0x58 [venus_core]
> load_scale_v4+0x228/0x2b4 [venus_core]
> session_process_buf+0x160/0x198 [venus_core]
> venus_helper_vb2_buf_queue+0xcc/0x130 [venus_core]
> vdec_vb2_buf_queue+0xc4/0x140 [venus_dec]
> __enqueue_in_driver+0x164/0x188 [videobuf2_common]
> vb2_core_qbuf+0x13c/0x47c [videobuf2_common]
> vb2_qbuf+0x88/0xec [videobuf2_v4l2]
> v4l2_m2m_qbuf+0x84/0x15c [v4l2_mem2mem]
> v4l2_m2m_ioctl_qbuf+0x24/0x30 [v4l2_mem2mem]
> v4l_qbuf+0x54/0x68
> __video_do_ioctl+0x2bc/0x3bc
> video_usercopy+0x558/0xb04
> video_ioctl2+0x24/0x30
> v4l2_ioctl+0x58/0x68
> v4l2_compat_ioctl32+0x84/0xa0
> __arm64_compat_sys_ioctl+0x12c/0x140
> invoke_syscall+0x54/0x110
> el0_svc_common+0x88/0xf0
> do_el0_svc_compat+0x28/0x34
> el0_svc_compat+0x24/0x34
> el0_sync_compat_handler+0xc0/0xf0
> el0_sync_compat+0x19c/0x1c0
>
> -> #0 (&inst->lock#3){+.+.}-{3:3}:
> __lock_acquire+0x248c/0x2d6c
> lock_acquire+0x240/0x314
> __mutex_lock_common+0xcc/0xb88
> mutex_lock_nested+0x5c/0x68
> vdec_buf_cleanup+0x3c/0x17c [venus_dec]
> __vb2_queue_free+0x98/0x204 [videobuf2_common]
> vb2_core_reqbufs+0x14c/0x390 [videobuf2_common]
> vb2_reqbufs+0x58/0x74 [videobuf2_v4l2]
> v4l2_m2m_reqbufs+0x58/0x90 [v4l2_mem2mem]
> v4l2_m2m_ioctl_reqbufs+0x24/0x30 [v4l2_mem2mem]
> v4l_reqbufs+0x58/0x6c
> __video_do_ioctl+0x2bc/0x3bc
> video_usercopy+0x558/0xb04
> video_ioctl2+0x24/0x30
> v4l2_ioctl+0x58/0x68
> v4l2_compat_ioctl32+0x84/0xa0
> __arm64_compat_sys_ioctl+0x12c/0x140
> invoke_syscall+0x54/0x110
> el0_svc_common+0x88/0xf0
> do_el0_svc_compat+0x28/0x34
> el0_svc_compat+0x24/0x34
> el0_sync_compat_handler+0xc0/0xf0
> el0_sync_compat+0x19c/0x1c0
>
> other info that might help us debug this:
>
> Chain exists of:
> &inst->lock#3 --> &mm->mmap_lock --> &q->mmap_lock
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&q->mmap_lock);
> lock(&mm->mmap_lock);
> lock(&q->mmap_lock);
> lock(&inst->lock#3);
>
> *** DEADLOCK ***
>
> 1 lock held by ThreadPoolSingl/3969:
> #0: ffffff80d3c3c4f8 (&q->mmap_lock){+.+.}-{3:3}, at: vb2_core_reqbufs+0xe4/0x390 [videobuf2_common]
>
> stack backtrace:
> CPU: 2 PID: 3969 Comm: ThreadPoolSingl Not tainted 5.13.0-rc2 #71
> Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
> Call trace:
> dump_backtrace+0x0/0x1b4
> show_stack+0x24/0x30
> dump_stack+0xe0/0x15c
> print_circular_bug+0x32c/0x388
> check_noncircular+0x138/0x140
> __lock_acquire+0x248c/0x2d6c
> lock_acquire+0x240/0x314
> __mutex_lock_common+0xcc/0xb88
> mutex_lock_nested+0x5c/0x68
> vdec_buf_cleanup+0x3c/0x17c [venus_dec]
> __vb2_queue_free+0x98/0x204 [videobuf2_common]
> vb2_core_reqbufs+0x14c/0x390 [videobuf2_common]
> vb2_reqbufs+0x58/0x74 [videobuf2_v4l2]
> v4l2_m2m_reqbufs+0x58/0x90 [v4l2_mem2mem]
> v4l2_m2m_ioctl_reqbufs+0x24/0x30 [v4l2_mem2mem]
> v4l_reqbufs+0x58/0x6c
> __video_do_ioctl+0x2bc/0x3bc
> video_usercopy+0x558/0xb04
> video_ioctl2+0x24/0x30
> v4l2_ioctl+0x58/0x68
> v4l2_compat_ioctl32+0x84/0xa0
> __arm64_compat_sys_ioctl+0x12c/0x140
> invoke_syscall+0x54/0x110
> el0_svc_common+0x88/0xf0
> do_el0_svc_compat+0x28/0x34
> el0_svc_compat+0x24/0x34
> el0_sync_compat_handler+0xc0/0xf0
> el0_sync_compat+0x19c/0x1c0
>
> The 'gpd_list_lock' is nominally named as such to protect the 'gpd_list'
> from concurrent access and mutation. Unfortunately, holding that mutex
> around various OPP framework calls leads to lockdep splats because now
> we're doing various operations in OPP core such as registering with
> debugfs while holding the list lock. We don't need to hold any list
> mutex while we're calling into OPP, so let's shrink the locking area of
> the 'gpd_list_lock' so that lockdep isn't triggered. This also helps
> reduce contention on this lock, which probably doesn't matter much but
> at least is nice to have.
>
> Cc: Len Brown <len.brown@intel.com>
> Cc: Pavel Machek <pavel@ucw.cz>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: <linux-pm@vger.kernel.org>
> Cc: Viresh Kumar <vireshk@kernel.org>
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>

Thanks for fixing this!

As I said, when discussing the previous version, I am working on
additional improvements, but this should be a step in the right
direction.

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe

> ---
>
> Changes from v1:
> * Removed list lock in genpd_add_provider() as it serves no purpose
>
> drivers/base/power/domain.c | 38 +++++++++++++++++--------------------
> 1 file changed, 17 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index b6a782c31613..03d18223d8bb 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -1984,8 +1984,8 @@ int pm_genpd_init(struct generic_pm_domain *genpd,
>
> mutex_lock(&gpd_list_lock);
> list_add(&genpd->gpd_list_node, &gpd_list);
> - genpd_debug_add(genpd);
> mutex_unlock(&gpd_list_lock);
> + genpd_debug_add(genpd);
>
> return 0;
> }
> @@ -2172,12 +2172,19 @@ static int genpd_add_provider(struct device_node *np, genpd_xlate_t xlate,
>
> static bool genpd_present(const struct generic_pm_domain *genpd)
> {
> + bool ret = false;
> const struct generic_pm_domain *gpd;
>
> - list_for_each_entry(gpd, &gpd_list, gpd_list_node)
> - if (gpd == genpd)
> - return true;
> - return false;
> + mutex_lock(&gpd_list_lock);
> + list_for_each_entry(gpd, &gpd_list, gpd_list_node) {
> + if (gpd == genpd) {
> + ret = true;
> + break;
> + }
> + }
> + mutex_unlock(&gpd_list_lock);
> +
> + return ret;
> }
>
> /**
> @@ -2188,15 +2195,13 @@ static bool genpd_present(const struct generic_pm_domain *genpd)
> int of_genpd_add_provider_simple(struct device_node *np,
> struct generic_pm_domain *genpd)
> {
> - int ret = -EINVAL;
> + int ret;
>
> if (!np || !genpd)
> return -EINVAL;
>
> - mutex_lock(&gpd_list_lock);
> -
> if (!genpd_present(genpd))
> - goto unlock;
> + return -EINVAL;
>
> genpd->dev.of_node = np;
>
> @@ -2207,7 +2212,7 @@ int of_genpd_add_provider_simple(struct device_node *np,
> if (ret != -EPROBE_DEFER)
> dev_err(&genpd->dev, "Failed to add OPP table: %d\n",
> ret);
> - goto unlock;
> + return ret;
> }
>
> /*
> @@ -2225,16 +2230,13 @@ int of_genpd_add_provider_simple(struct device_node *np,
> dev_pm_opp_of_remove_table(&genpd->dev);
> }
>
> - goto unlock;
> + return ret;
> }
>
> genpd->provider = &np->fwnode;
> genpd->has_provider = true;
>
> -unlock:
> - mutex_unlock(&gpd_list_lock);
> -
> - return ret;
> + return 0;
> }
> EXPORT_SYMBOL_GPL(of_genpd_add_provider_simple);
>
> @@ -2253,8 +2255,6 @@ int of_genpd_add_provider_onecell(struct device_node *np,
> if (!np || !data)
> return -EINVAL;
>
> - mutex_lock(&gpd_list_lock);
> -
> if (!data->xlate)
> data->xlate = genpd_xlate_onecell;
>
> @@ -2294,8 +2294,6 @@ int of_genpd_add_provider_onecell(struct device_node *np,
> if (ret < 0)
> goto error;
>
> - mutex_unlock(&gpd_list_lock);
> -
> return 0;
>
> error:
> @@ -2314,8 +2312,6 @@ int of_genpd_add_provider_onecell(struct device_node *np,
> }
> }
>
> - mutex_unlock(&gpd_list_lock);
> -
> return ret;
> }
> EXPORT_SYMBOL_GPL(of_genpd_add_provider_onecell);
>
> base-commit: d07f6ca923ea0927a1024dfccafc5b53b61cfecc
> --
> https://chromeos.dev
>

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