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@xxxxxxxxxxxxxxxxxx>
Tested-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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