On Wed, Jul 07, 2021 at 04:36:49PM +0000, Roberto Sassu wrote:
Hi
I'm getting this oops (on commit a180bd1d7e16):
[ 17.711520] BUG: kernel NULL pointer dereference, address: 0000000000000010 [ 17.739451] RIP: 0010:qxl_bo_move_notify+0x35/0x80 [qxl] [ 17.827345] RSP: 0018:ffffc90000457c08 EFLAGS: 00010286 [ 17.827350] RAX: 0000000000000001 RBX: 0000000000000000 RCX: dffffc0000000000 [ 17.827353] RDX: 0000000000000007 RSI: 0000000000000004 RDI: ffffffff85596feb [ 17.827356] RBP: ffff88800e311c00 R08: 0000000000000000 R09: 0000000000000000 [ 17.827358] R10: ffffffff8697b243 R11: fffffbfff0d2f648 R12: 0000000000000000 [ 17.827361] R13: ffff88800e311e48 R14: ffff88800e311e98 R15: ffff88800e311e90 [ 17.827364] FS: 0000000000000000(0000) GS:ffff88805d800000(0000) knlGS:0000000000000000 [ 17.861699] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 17.861703] CR2: 0000000000000010 CR3: 000000002642c000 CR4: 0000000000350ee0 [ 17.861707] Call Trace: [ 17.861712] ttm_bo_cleanup_memtype_use+0x4d/0xb0 [ttm] [ 17.861730] ttm_bo_release+0x42d/0x7c0 [ttm] [ 17.861746] ? ttm_bo_cleanup_refs+0x127/0x420 [ttm] [ 17.888300] ttm_bo_delayed_delete+0x289/0x390 [ttm] [ 17.888317] ? ttm_bo_cleanup_refs+0x420/0x420 [ttm] [ 17.888332] ? lock_release+0x9c/0x5c0 [ 17.901033] ? rcu_read_lock_held_common+0x1a/0x50 [ 17.905183] ttm_device_delayed_workqueue+0x18/0x50 [ttm] [ 17.909371] process_one_work+0x537/0x9f0 [ 17.913345] ? pwq_dec_nr_in_flight+0x160/0x160 [ 17.917297] ? lock_acquired+0xa4/0x580 [ 17.921168] ? worker_thread+0x169/0x600 [ 17.925034] worker_thread+0x7a/0x600 [ 17.928657] ? process_one_work+0x9f0/0x9f0 [ 17.932360] kthread+0x200/0x230 [ 17.935930] ? set_kthread_struct+0x80/0x80 [ 17.939593] ret_from_fork+0x22/0x30 [ 17.951737] CR2: 0000000000000010 [ 17.955496] ---[ end trace e30cc21c24e81ee5 ]---I had a look at the code, and it seems that this is caused by trying to use bo->resource which is NULL.
bo->resource is freed by ttm_bo_cleanup_refs() -> ttm_bo_cleanup_memtype_use() -> ttm_resource_free().
And then a notification is issued by ttm_bo_cleanup_refs() -> ttm_bo_put() -> ttm_bo_release() -> ttm_bo_cleanup_memtype_use(), this time with bo->release equal to NULL.
I was thinking a proper way to fix this. Checking that bo->release is not NULL in qxl_bo_move_notify() would solve the issue. But maybe there is a better way, like avoiding that ttm_bo_cleanup_memtype_use() is called twice. Which way would be preferable?
Adding Christian and Dave, who've touched all this recently iirc. -Daniel
Thanks
Roberto
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