Messages in this thread | | | Subject | Re: [PATCH v4 10/19] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() | From | Qian Cai <> | Date | Thu, 12 Nov 2020 11:38:51 -0500 |
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On Fri, 2020-10-23 at 12:12 +0200, Peter Zijlstra wrote: > Concurrent migrate_disable() and set_cpus_allowed_ptr() has > interesting features. We rely on set_cpus_allowed_ptr() to not return > until the task runs inside the provided mask. This expectation is > exported to userspace. > > This means that any set_cpus_allowed_ptr() caller must wait until > migrate_enable() allows migrations. > > At the same time, we don't want migrate_enable() to schedule, due to > patterns like: > > preempt_disable(); > migrate_disable(); > ... > migrate_enable(); > preempt_enable(); > > And: > > raw_spin_lock(&B); > spin_unlock(&A); > > this means that when migrate_enable() must restore the affinity > mask, it cannot wait for completion thereof. Luck will have it that > that is exactly the case where there is a pending > set_cpus_allowed_ptr(), so let that provide storage for the async stop > machine. > > Much thanks to Valentin who used TLA+ most effective and found lots of > 'interesting' cases. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > include/linux/sched.h | 1 > kernel/sched/core.c | 234 +++++++++++++++++++++++++++++++++++++++++++----- > -- > 2 files changed, 205 insertions(+), 30 deletions(-)
Some syscall fuzzing from an unprivileged user starts to trigger this below since this commit first appeared in the linux-next today. Does it ring any bells?
[12065.065837][ T1310] INFO: task trinity-c30:91730 blocked for more than 368 seconds. [12065.073524][ T1310] Tainted: G L 5.10.0-rc3-next-20201112 #2 [12065.081076][ T1310] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [12065.089648][ T1310] task:trinity-c30 state:D stack:26576 pid:91730 ppid: 82688 flags:0x00000000 [12065.098818][ T1310] Call trace: [12065.101987][ T1310] __switch_to+0xf0/0x1a8 [12065.106227][ T1310] __schedule+0x6ec/0x1708 [12065.110505][ T1310] schedule+0x1bc/0x3b0 [12065.114562][ T1310] schedule_timeout+0x3c4/0x4c0 [12065.119275][ T1310] wait_for_completion+0x13c/0x248 [12065.124257][ T1310] affine_move_task+0x410/0x688 (inlined by) affine_move_task at kernel/sched/core.c:2261 [12065.129013][ T1310] __set_cpus_allowed_ptr+0x1b4/0x370 [12065.134248][ T1310] sched_setaffinity+0x4f0/0x7e8 [12065.139088][ T1310] __arm64_sys_sched_setaffinity+0x1f4/0x2a0 [12065.144972][ T1310] do_el0_svc+0x124/0x228 [12065.149165][ T1310] el0_sync_handler+0x208/0x384 [12065.153876][ T1310] el0_sync+0x140/0x180 [12065.157971][ T1310] [12065.157971][ T1310] Showing all locks held in the system: [12065.166401][ T1310] 1 lock held by khungtaskd/1310: [12065.171288][ T1310] #0: ffff800018d0cb40 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire.constprop.56+0x0/0x38 [12065.182210][ T1310] 4 locks held by trinity-main/82688: [12065.187515][ T1310] 2 locks held by kworker/u513:3/82813: [12065.192922][ T1310] #0: ffff000000419d38 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x69c/0x18c8 [12065.203890][ T1310] #1: ffff0000122bfd40 ((work_completion)(&buf->work)){+.+.}-{0:0}, at: __update_idle_core+0xa8/0x460 [12065.214916][ T1310] 1 lock held by trinity-c35/137168: [12065.220061][ T1310] #0: ffff0087ce767898 (&tty->ldisc_sem){++++}-{0:0}, at: ldsem_down_read+0x3c/0x48 [12065.229483][ T1310] 3 locks held by trinity-c61/137611: [12065.234757][ T1310] 1 lock held by trinity-c7/137630: [12065.239828][ T1310] 1 lock held by trinity-c57/137714: [12065.242612][T137611] futex_wake_op: trinity-c61 tries to shift op by 1008; fix this program [12065.245012][ T1310] 1 lock held by trinity-c52/137771: [12065.258538][ T1310] 2 locks held by trinity-c42/137835: [12065.263783][ T1310] 4 locks held by trinity-c22/137868: [12065.269051][ T1310] #0: ffff000e78503798 (&rq->lock){-.-.}-{2:2}, at: newidle_balance+0x92c/0xd78 [12065.278155][ T1310] #1: ffff0087ce767930 (&tty->atomic_write_lock){+.+.}-{3:3}, at: tty_write_lock+0x30/0x58 [12065.288317][ T1310] #2: ffff800018d0cb40 (rcu_read_lock){....}-{1:2}, at: __mutex_lock+0x24c/0x1310 [12065.297592][ T1310] #3: ffff800018d0cb40 (rcu_read_lock){....}-{1:2}, at: lock_page_memcg+0x98/0x240 [12065.307026][ T1310] 2 locks held by trinity-c34/137896: [12065.312266][ T1310] #0: ffff000e78463798 (&rq->lock){-.-.}-{2:2}, at: __schedule+0x22c/0x1708 [12065.321023][ T1310] #1: ffff800018d0cb40 (rcu_read_lock){....}-{1:2}, at: __update_idle_core+0xa8/0x460 [12065.330663][ T1310] 2 locks held by trinity-c43/137909: [12065.335996][ T1310] 1 lock held by trinity-c24/137910: [12065.341164][ T1310] 1 lock held by trinity-c1/137954: [12065.346272][ T1310] 1 lock held by trinity-c49/138020: [12065.351425][ T1310] 1 lock held by trinity-c10/138021: [12065.356649][ T1310] 1 lock held by trinity-c32/138039: [12065.361813][ T1310] 4 locks held by trinity-c36/138042: [12065.367129][ T1310] 2 locks held by trinity-c14/138061: [12065.372378][ T1310] 2 locks held by trinity-c38/138070: [12065.377688][ T1310] 1 lock held by trinity-c50/138074: [12065.382885][ T1310] 1 lock held by trinity-c12/138085: [12065.388186][ T1310] 1 lock held by trinity-c4/138087: [12065.393272][ T1310] 3 locks held by trinity-c6/138091: [12065.398492][ T1310] 2 locks held by trinity-c48/138095: [12065.403757][ T1310] 2 locks held by trinity-c62/138097: [12065.409045][ T1310] 2 locks held by trinity-main/138107: [12065.414441][ T1310] 1 lock held by modprobe/138108: [12065.419351][ T1310] [12065.421560][ T1310] ============================================= [12065.421560][ T1310]
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