On Tue, Jun 28, 2022 at 5:51 AM Dmitry Osipenko dmitry.osipenko@collabora.com wrote:
On 6/28/22 15:31, Robin Murphy wrote:
----->8----- [ 68.295951] ====================================================== [ 68.295956] WARNING: possible circular locking dependency detected [ 68.295963] 5.19.0-rc3+ #400 Not tainted [ 68.295972] ------------------------------------------------------ [ 68.295977] cc1/295 is trying to acquire lock: [ 68.295986] ffff000008d7f1a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_shmem_free+0x7c/0x198 [ 68.296036] [ 68.296036] but task is already holding lock: [ 68.296041] ffff80000c14b820 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0x4d8/0x1470 [ 68.296080] [ 68.296080] which lock already depends on the new lock. [ 68.296080] [ 68.296085] [ 68.296085] the existing dependency chain (in reverse order) is: [ 68.296090] [ 68.296090] -> #1 (fs_reclaim){+.+.}-{0:0}: [ 68.296111] fs_reclaim_acquire+0xb8/0x150 [ 68.296130] dma_resv_lockdep+0x298/0x3fc [ 68.296148] do_one_initcall+0xe4/0x5f8 [ 68.296163] kernel_init_freeable+0x414/0x49c [ 68.296180] kernel_init+0x2c/0x148 [ 68.296195] ret_from_fork+0x10/0x20 [ 68.296207] [ 68.296207] -> #0 (reservation_ww_class_mutex){+.+.}-{3:3}: [ 68.296229] __lock_acquire+0x1724/0x2398 [ 68.296246] lock_acquire+0x218/0x5b0 [ 68.296260] __ww_mutex_lock.constprop.0+0x158/0x2378 [ 68.296277] ww_mutex_lock+0x7c/0x4d8 [ 68.296291] drm_gem_shmem_free+0x7c/0x198 [ 68.296304] panfrost_gem_free_object+0x118/0x138 [ 68.296318] drm_gem_object_free+0x40/0x68 [ 68.296334] drm_gem_shmem_shrinker_run_objects_scan+0x42c/0x5b8 [ 68.296352] drm_gem_shmem_shrinker_scan_objects+0xa4/0x170 [ 68.296368] do_shrink_slab+0x220/0x808 [ 68.296381] shrink_slab+0x11c/0x408 [ 68.296392] shrink_node+0x6ac/0xb90 [ 68.296403] do_try_to_free_pages+0x1dc/0x8d0 [ 68.296416] try_to_free_pages+0x1ec/0x5b0 [ 68.296429] __alloc_pages_slowpath.constprop.0+0x528/0x1470 [ 68.296444] __alloc_pages+0x4e0/0x5b8 [ 68.296455] __folio_alloc+0x24/0x60 [ 68.296467] vma_alloc_folio+0xb8/0x2f8 [ 68.296483] alloc_zeroed_user_highpage_movable+0x58/0x68 [ 68.296498] __handle_mm_fault+0x918/0x12a8 [ 68.296513] handle_mm_fault+0x130/0x300 [ 68.296527] do_page_fault+0x1d0/0x568 [ 68.296539] do_translation_fault+0xa0/0xb8 [ 68.296551] do_mem_abort+0x68/0xf8 [ 68.296562] el0_da+0x74/0x100 [ 68.296572] el0t_64_sync_handler+0x68/0xc0 [ 68.296585] el0t_64_sync+0x18c/0x190 [ 68.296596] [ 68.296596] other info that might help us debug this: [ 68.296596] [ 68.296601] Possible unsafe locking scenario: [ 68.296601] [ 68.296604] CPU0 CPU1 [ 68.296608] ---- ---- [ 68.296612] lock(fs_reclaim); [ 68.296622] lock(reservation_ww_class_mutex); [ 68.296633] lock(fs_reclaim); [ 68.296644] lock(reservation_ww_class_mutex); [ 68.296654] [ 68.296654] *** DEADLOCK ***
This splat could be ignored for now. I'm aware about it, although haven't looked closely at how to fix it since it's a kind of a lockdep misreporting.
The lockdep splat could be fixed with something similar to what I've done in msm, ie. basically just not acquire the lock in the finalizer:
https://patchwork.freedesktop.org/patch/489364/
There is one gotcha to watch for, as danvet pointed out (scan_objects() could still see the obj in the LRU before the finalizer removes it), but if scan_objects() does the kref_get_unless_zero() trick, it is safe.
BR, -R