[PATCH] dma_resv: prime lockdep annotations

[Chris Wilson]

Quoting Daniel Vetter (2019-08-22 07:54:57)
> +#if IS_ENABLED(CONFIG_LOCKDEP)
> +static void dma_resv_lockdep(void)
> +{
> +       struct mm_struct *mm = mm_alloc();
> +       struct dma_resv obj;
> +
> +       if (!mm)
> +               return;
> +
> +       dma_resv_init(&obj);
> +
> +       down_read(&mm->mmap_sem);
> +       ww_mutex_lock(&obj.lock, NULL);
> +       fs_reclaim_acquire(GFP_KERNEL);
> +       fs_reclaim_release(GFP_KERNEL);
> +       ww_mutex_unlock(&obj.lock);
> +       up_read(&mm->mmap_sem);
> +       
> +       mmput(mm);
> +}
> +subsys_initcall(dma_resv_lockdep);
> +#endif

Adding a

	dma_resv_lock();
	might_lock(&i915->drm.struct_mutex);
	dma_resv_unlock();

yielded

[   18.513633] ======================================================
[   18.513636] WARNING: possible circular locking dependency detected
[   18.513639] 5.3.0-rc5+ #76 Not tainted
[   18.513640] ------------------------------------------------------
[   18.513643] insmod/655 is trying to acquire lock:
[   18.513645] 00000000877909e7 (&dev->struct_mutex){+.+.}, at: i915_driver_probe+0x89c/0x1470 [i915]
[   18.513671] 
[   18.513671] but task is already holding lock:
[   18.513673] 00000000a85ba8ec (reservation_ww_class_mutex){+.+.}, at: i915_driver_probe+0x8e1/0x1470 [i915]
[   18.513698] 
[   18.513698] which lock already depends on the new lock.
[   18.513698] 
[   18.513701] 
[   18.513701] the existing dependency chain (in reverse order) is:
[   18.513703] 
[   18.513703] -> #1 (reservation_ww_class_mutex){+.+.}:
[   18.513708]        __ww_mutex_lock.constprop.17+0xbc/0xf90
[   18.513739]        i915_gem_init+0x518/0x750 [i915]
[   18.513762]        i915_driver_probe+0x891/0x1470 [i915]
[   18.513785]        i915_pci_probe+0x2f/0x110 [i915]
[   18.513789]        pci_device_probe+0x99/0x110
[   18.513792]        really_probe+0xd1/0x360
[   18.513794]        driver_probe_device+0xaf/0xf0
[   18.513796]        device_driver_attach+0x4a/0x50
[   18.513799]        __driver_attach+0x80/0x140
[   18.513801]        bus_for_each_dev+0x5e/0x90
[   18.513804]        bus_add_driver+0x148/0x1e0
[   18.513806]        driver_register+0x66/0xb0
[   18.513809]        do_one_initcall+0x45/0x29f
[   18.513812]        do_init_module+0x55/0x200
[   18.513814]        load_module+0x2519/0x2690
[   18.513816]        __do_sys_finit_module+0x8f/0xd0
[   18.513818]        do_syscall_64+0x4f/0x220
[   18.513822]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   18.513824] 
[   18.513824] -> #0 (&dev->struct_mutex){+.+.}:
[   18.513828]        __lock_acquire+0xcb9/0x1520
[   18.513831]        lock_acquire+0x90/0x170
[   18.513853]        i915_driver_probe+0x8fd/0x1470 [i915]
[   18.513876]        i915_pci_probe+0x2f/0x110 [i915]
[   18.513879]        pci_device_probe+0x99/0x110
[   18.513881]        really_probe+0xd1/0x360
[   18.513883]        driver_probe_device+0xaf/0xf0
[   18.513886]        device_driver_attach+0x4a/0x50
[   18.513888]        __driver_attach+0x80/0x140
[   18.513891]        bus_for_each_dev+0x5e/0x90
[   18.513893]        bus_add_driver+0x148/0x1e0
[   18.513895]        driver_register+0x66/0xb0
[   18.513897]        do_one_initcall+0x45/0x29f
[   18.513899]        do_init_module+0x55/0x200
[   18.513902]        load_module+0x2519/0x2690
[   18.513904]        __do_sys_finit_module+0x8f/0xd0
[   18.513906]        do_syscall_64+0x4f/0x220
[   18.513909]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   18.513911] 
[   18.513911] other info that might help us debug this:
[   18.513911] 
[   18.513914]  Possible unsafe locking scenario:
[   18.513914] 
[   18.513916]        CPU0                    CPU1
[   18.513918]        ----                    ----
[   18.513920]   lock(reservation_ww_class_mutex);
[   18.513922]                                lock(&dev->struct_mutex);
[   18.513924]                                lock(reservation_ww_class_mutex);
[   18.513927]   lock(&dev->struct_mutex);
[   18.513929] 
[   18.513929]  *** DEADLOCK ***
[   18.513929] 
[   18.513932] 3 locks held by insmod/655:
[   18.513933]  #0: 000000004dccb591 (&dev->mutex){....}, at: device_driver_attach+0x18/0x50
[   18.513938]  #1: 000000009118ecae (&mm->mmap_sem#2){++++}, at: i915_driver_probe+0x8c8/0x1470 [i915]
[   18.513962]  #2: 00000000a85ba8ec (reservation_ww_class_mutex){+.+.}, at: i915_driver_probe+0x8e1/0x1470 [i915]

so

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
Tested-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris