Messages in this thread | | | Subject | Re: [RFC PATCH v2 2/2] blk-mq: Lockout tagset iter when freeing rqs | From | John Garry <> | Date | Wed, 23 Dec 2020 11:40:38 +0000 |
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- ppvk@codeaurora.org
> >> Are there any blk_mq_tagset_busy_iter() calls that happen from a >> context where the tag set can disappear while that function is in >> progress? >> > > So isn't the blk_mq_tag_set always a member of the host driver data for > those cases, and, since blk_mq_tagset_busy_iter() is for iter'ing block > driver tags and called from block driver or hctx_busy_show(), it would > exist for the lifetime of the host device. > >> Some blk_mq_tagset_busy_iter() calls happen from a context where it is >> not allowed to sleep but also where it is guaranteed that the tag set >> won't disappear, e.g. the call from inside sdk_mq_queue_rq(). > > You're talking about skd_mq_queue_rq() -> skd_in_flight() -> > blk_mq_tagset_busy_iter(), right? > > So I would expect any .queue_rq calls to complete before the associated > request queue and tagset may be unregistered. > >> >> How about using a mutex inside blk_mq_queue_tag_busy_iter() instead? >> As far as I can see all blk_mq_queue_tag_busy_iter() happen from a >> context where it is allowed to sleep. > > Well then it seems sensible to add might_sleep() also. > > And we still have the blk_mq_queue_tag_busy_iter() problem. As Ming > mentioned yesterday, we know contexts where from where it is called > which may not sleep.
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.
Thanks, John
[0] https://lore.kernel.org/linux-block/9d4124ea-dbab-41cf-63bd-b17ef3e5037a@huawei.com/
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