On 2/4/21 2:20 AM, Xiaoguang Wang wrote: > Abaci Robot reported following panic: > BUG: kernel NULL pointer dereference, address: 0000000000000000 > PGD 800000010ef3f067 P4D 800000010ef3f067 PUD 10d9df067 PMD 0 > Oops: 0002 [#1] SMP PTI > CPU: 0 PID: 1869 Comm: io_wqe_worker-0 Not tainted 5.11.0-rc3+ #1 > Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011 > RIP: 0010:put_files_struct+0x1b/0x120 > Code: 24 18 c7 00 f4 ff ff ff e9 4d fd ff ff 66 90 0f 1f 44 00 00 41 57 41 56 49 89 fe 41 55 41 54 55 53 48 83 ec 08 e8 b5 6b db ff 41 ff 0e 74 13 48 83 c4 08 5b 5d 41 5c 41 5d 41 5e 41 5f e9 9c > RSP: 0000:ffffc90002147d48 EFLAGS: 00010293 > RAX: 0000000000000000 RBX: ffff88810d9a5300 RCX: 0000000000000000 > RDX: ffff88810d87c280 RSI: ffffffff8144ba6b RDI: 0000000000000000 > RBP: 0000000000000080 R08: 0000000000000001 R09: ffffffff81431500 > R10: ffff8881001be000 R11: 0000000000000000 R12: ffff88810ac2f800 > R13: ffff88810af38a00 R14: 0000000000000000 R15: ffff8881057130c0 > FS: 0000000000000000(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000000 CR3: 000000010dbaa002 CR4: 00000000003706f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > __io_clean_op+0x10c/0x2a0 > io_dismantle_req+0x3c7/0x600 > __io_free_req+0x34/0x280 > io_put_req+0x63/0xb0 > io_worker_handle_work+0x60e/0x830 > ? io_wqe_worker+0x135/0x520 > io_wqe_worker+0x158/0x520 > ? __kthread_parkme+0x96/0xc0 > ? io_worker_handle_work+0x830/0x830 > kthread+0x134/0x180 > ? kthread_create_worker_on_cpu+0x90/0x90 > ret_from_fork+0x1f/0x30 > Modules linked in: > CR2: 0000000000000000 > ---[ end trace c358ca86af95b1e7 ]--- > > I guess case below can trigger above panic: there're two threads which > operates different io_uring ctxs and share same sqthread identity, and > later one thread exits, io_uring_cancel_task_requests() will clear > task->io_uring->identity->files to be NULL in sqpoll mode, then another > ctx that uses same identity will panic. > > Indeed we don't need to clear task->io_uring->identity->files here, > io_grab_identity() should handle identity->files changes well, if > task->io_uring->identity->files is not equal to current->files, > io_cow_identity() should handle this changes well. Applied, thanks. -- Jens Axboe
