blk-iocost: use irq-safe locking in cgroup handlers#913
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ioc_timer_fn() acquires ioc->lock from timer softirq context. The io.weight, io.cost.qos and io.cost.model cgroup handlers can take the same lock from process context, and the direct handler paths must not do so with interrupts enabled. A blkcg policy configuration reproducer with lockdep reproduced the following report: WARNING: inconsistent lock state 7.1.0-rc2-g1e14adca0199 #1 Not tainted -------------------------------- inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. swapper/2/0 [HC0[0]:SC1[1]:HE0:SE0] takes: ffff88810f95d0f8 (&ioc->lock){+.?.}-{3:3}, at: ioc_timer_fn+0x3ff/0x3af0 {SOFTIRQ-ON-W} state was registered at: lock_acquire+0xd4/0x290 _raw_spin_lock+0x3a/0x70 ioc_weight_write+0x35a/0x420 cgroup_file_write+0x1c5/0x4b0 kernfs_fop_write_iter+0x1d7/0x280 vfs_write+0x580/0x630 ksys_write+0xec/0x190 do_syscall_64+0x156/0x490 entry_SYSCALL_64_after_hwframe+0x77/0x7f Possible unsafe locking scenario: CPU0 ---- lock(&ioc->lock); <Interrupt> lock(&ioc->lock); *** DEADLOCK *** 1 lock held by swapper/2/0: #0: ffffc90000230d20 ((&ioc->timer)){+.-.}-{0:0}, at: call_timer_fn+0xba/0x3a0 stack backtrace: CPU: 2 UID: 0 PID: 0 Comm: swapper/2 Not tainted 7.1.0-rc2-g1e14adca0199 #1 PREEMPT ea13f83d4b74a12510d20db4a7d9a0fe8275f05c Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-5.fc42 04/01/2014 Call Trace: <IRQ> dump_stack_lvl+0x54/0x70 print_usage_bug+0x26d/0x280 mark_lock_irq+0x3ef/0x400 mark_lock+0x117/0x190 __lock_acquire+0x592/0x2850 lock_acquire+0xd4/0x290 _raw_spin_lock_irq+0x49/0x80 ioc_timer_fn+0x3ff/0x3af0 call_timer_fn+0x120/0x3a0 __run_timer_base+0x3ad/0x490 run_timer_softirq+0x31/0x60 handle_softirqs+0x1a0/0x550 __irq_exit_rcu+0x8c/0x150 irq_exit_rcu+0xe/0x20 sysvec_apic_timer_interrupt+0x6e/0x80 </IRQ> Use spin_lock_irq() in the affected process-context handlers. The default io.weight update already holds blkcg->lock with spin_lock_irq(), so the nested ioc->lock acquisition there is already IRQ-safe and is left as a plain spin_lock(). Fixes: 7caa471 ("blkcg: implement blk-iocost") Signed-off-by: Yu Kuai <yukuai@fygo.io>
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Pull request for series with
subject: blk-iocost: use irq-safe locking in cgroup handlers
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1103769