On 12/23/20 3:40 AM, John Garry wrote: > Sorry, I got the 2x iter functions mixed up. > > So if we use mutex to solve blk_mq_queue_tag_busy_iter() problem, then we > still have this issue in blk_mq_tagset_busy_iter() which I report previously > [0]: > > [ 319.771745] BUG: KASAN: use-after-free in bt_tags_iter+0xe0/0x128 > [ 319.777832] Read of size 4 at addr ffff0010b6bd27cc by task more/1866 > [ 319.784262] > [ 319.785753] CPU: 61 PID: 1866 Comm: more Tainted: G W > 5.10.0-rc4-18118-gaa7b9c30d8ff #1070 > [ 319.795312] Hardware name: Huawei Taishan 2280 /D05, BIOS Hisilicon > D05 IT21 Nemo 2.0 RC0 04/18/2018 > [ 319.804437] Call trace: > [ 319.806892] dump_backtrace+0x0/0x2d0 > [ 319.810552] show_stack+0x18/0x68 > [ 319.813865] dump_stack+0x100/0x16c > [ 319.817348] print_address_description.constprop.12+0x6c/0x4e8 > [ 319.823176] kasan_report+0x130/0x200 > [ 319.826831] __asan_load4+0x9c/0xd8 > [ 319.830315] bt_tags_iter+0xe0/0x128 > [ 319.833884] __blk_mq_all_tag_iter+0x320/0x3a8 > [ 319.838320] blk_mq_tagset_busy_iter+0x8c/0xd8 > [ 319.842760] scsi_host_busy+0x88/0xb8 > [ 319.846418] show_host_busy+0x1c/0x48 > [ 319.850079] dev_attr_show+0x44/0x90 > [ 319.853655] sysfs_kf_seq_show+0x128/0x1c8 > [ 319.857744] kernfs_seq_show+0xa0/0xb8 > [ 319.861489] seq_read_iter+0x1ec/0x6a0 > [ 319.865230] seq_read+0x1d0/0x250 > [ 319.868539] kernfs_fop_read+0x70/0x330 > [ 319.872369] vfs_read+0xe4/0x250 > [ 319.875590] ksys_read+0xc8/0x178 > [ 319.878898] __arm64_sys_read+0x44/0x58 > [ 319.882730] el0_svc_common.constprop.2+0xc4/0x1e8 > [ 319.887515] do_el0_svc+0x90/0xa0 > [ 319.890824] el0_sync_handler+0x128/0x178 > [ 319.894825] el0_sync+0x158/0x180 > [ 319.898131] > [ 319.899614] The buggy address belongs to the page: > [ 319.904403] page:000000004e9e6864 refcount:0 mapcount:0 > mapping:0000000000000000 index:0x0 pfn:0x10b6bd2 > [ 319.913876] flags: 0xbfffc0000000000() > [ 319.917626] raw: 0bfffc0000000000 0000000000000000 fffffe0000000000 > 0000000000000000 > [ 319.925363] raw: 0000000000000000 0000000000000000 00000000ffffffff > 0000000000000000 > [ 319.933096] page dumped because: kasan: bad access detected > [ 319.938658] > [ 319.940141] Memory state around the buggy address: > [ 319.944925] ffff0010b6bd2680: ff ff ff ff ff ff ff ff ff ff ff ff ff > ff ff ff > [ 319.952139] ffff0010b6bd2700: ff ff ff ff ff ff ff ff ff ff ff ff ff > ff ff ff > [ 319.959354] >ffff0010b6bd2780: ff ff ff ff ff ff ff ff ff ff ff ff ff > ff ff ff > [ 319.966566] ^ > [ 319.972131] ffff0010b6bd2800: ff ff ff ff ff ff ff ff ff ff ff ff ff > ff ff ff > [ 319.979344] ffff0010b6bd2880: ff ff ff ff ff ff ff ff ff ff ff ff ff > ff ff ff > [ 319.986557] > ================================================================== > [ 319.993770] Disabling lock debugging due to kernel taint > > So to trigger this, I start fio on a disk, and then have one script > which constantly enables and disables an IO scheduler for that disk, and > another script which constantly reads /sys/class/scsi_host/host0/host_busy . > > And in this problem, the driver tag we iterate may point to a stale IO sched > request. Hi John, I propose to change the order in which blk_mq_sched_free_requests(q) and blk_mq_debugfs_unregister(q) are called. Today blk_mq_sched_free_requests(q) is called by blk_cleanup_queue() before blk_put_queue() is called. blk_put_queue() calls blk_release_queue() if the last reference is dropped. blk_release_queue() calls blk_mq_debugfs_unregister(). I prefer removing the debugfs attributes earlier over modifying the tag iteration functions because I think removing the debugfs attributes earlier is less risky. Although this will make it harder to debug lockups that happen while removing a request queue, kernel developers who are analyzing such an issue can undo this change in their development kernel tree. Thanks, Bart.
