scx: Fix raciness in scx_ops_bypass()
scx_ops_bypass() can currently race on the ops enable / disable path as
follows:
1. scx_ops_bypass(true) called on enable path, bypass depth is set to 1
2. An op on the init path exits, which schedules scx_ops_disable_workfn()
3. scx_ops_bypass(false) is called on the disable path, and bypass depth
is decremented to 0
4. kthread is scheduled to execute scx_ops_disable_workfn()
5. scx_ops_bypass(true) called, bypass depth set to 1
6. scx_ops_bypass() races when iterating over CPUs
While it's not safe to take any blocking locks on the bypass path, it is
safe to take a raw spinlock which cannot be preempted. This patch therefore
updates scx_ops_bypass() to use a raw spinlock to synchronize, and changes
scx_ops_bypass_depth to be a regular int.
Without this change, we observe the following warnings when running the
'exit' sched_ext selftest (sometimes requires a couple of runs):
.[root@virtme-ng sched_ext]# ./runner -t exit
===== START =====
TEST: exit
...
[ 14.935078] WARNING: CPU: 2 PID: 360 at kernel/sched/ext.c:4332 scx_ops_bypass+0x1ca/0x280
[ 14.935126] Modules linked in:
[ 14.935150] CPU: 2 UID: 0 PID: 360 Comm: sched_ext_ops_h Not tainted 6.11.0-virtme #24
[ 14.935192] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
[ 14.935242] Sched_ext: exit (enabling+all)
[ 14.935244] RIP: 0010:scx_ops_bypass+0x1ca/0x280
[ 14.935300] Code: ff ff ff e8 48 96 10 00 fb e9 08 ff ff ff c6 05 7b 34 e8 01 01 90 48 c7 c7 89 86 88 87 e8 be 1d f8 ff 90 0f 0b 90 90 eb 95 90 <0f> 0b 90 41 8b 84 24 24 0a 00 00 eb 97 90 0f 0b 90 41 8b 84 24 24
[ 14.935394] RSP: 0018:ffffb706c0957ce0 EFLAGS: 00010002
[ 14.935424] RAX: 0000000000000009 RBX: 0000000000000001 RCX: 00000000e3fb8b2a
[ 14.935465] RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff88a4c080
[ 14.935512] RBP: 0000000000009b56 R08: 0000000000000004 R09: 00000003f12e520a
[ 14.935555] R10: ffffffff863a9795 R11: 0000000000000000 R12: ffff8fc5fec31300
[ 14.935598] R13: ffff8fc5fec31318 R14: 0000000000000286 R15: 0000000000000018
[ 14.935642] FS: 0000000000000000(0000) GS:ffff8fc5fe680000(0000) knlGS:0000000000000000
[ 14.935684] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 14.935721] CR2: 0000557d92890b88 CR3: 000000002464a000 CR4: 0000000000750ef0
[ 14.935765] PKRU: 55555554
[ 14.935782] Call Trace:
[ 14.935802] <TASK>
[ 14.935823] ? __warn+0xce/0x220
[ 14.935850] ? scx_ops_bypass+0x1ca/0x280
[ 14.935881] ? report_bug+0xc1/0x160
[ 14.935909] ? handle_bug+0x61/0x90
[ 14.935934] ? exc_invalid_op+0x1a/0x50
[ 14.935959] ? asm_exc_invalid_op+0x1a/0x20
[ 14.935984] ? raw_spin_rq_lock_nested+0x15/0x30
[ 14.936019] ? scx_ops_bypass+0x1ca/0x280
[ 14.936046] ? srso_alias_return_thunk+0x5/0xfbef5
[ 14.936081] ? __pfx_scx_ops_disable_workfn+0x10/0x10
[ 14.936111] scx_ops_disable_workfn+0x146/0xac0
[ 14.936142] ? finish_task_switch+0xa9/0x2c0
[ 14.936172] ? srso_alias_return_thunk+0x5/0xfbef5
[ 14.936211] ? __pfx_scx_ops_disable_workfn+0x10/0x10
[ 14.936244] kthread_worker_fn+0x101/0x2c0
[ 14.936268] ? __pfx_kthread_worker_fn+0x10/0x10
[ 14.936299] kthread+0xec/0x110
[ 14.936327] ? __pfx_kthread+0x10/0x10
[ 14.936351] ret_from_fork+0x37/0x50
[ 14.936374] ? __pfx_kthread+0x10/0x10
[ 14.936400] ret_from_fork_asm+0x1a/0x30
[ 14.936427] </TASK>
[ 14.936443] irq event stamp: 21002
[ 14.936467] hardirqs last enabled at (21001): [<ffffffff863aa35f>] resched_cpu+0x9f/0xd0
[ 14.936521] hardirqs last disabled at (21002): [<ffffffff863dd0ba>] scx_ops_bypass+0x11a/0x280
[ 14.936571] softirqs last enabled at (20642): [<ffffffff863683d7>] __irq_exit_rcu+0x67/0xd0
[ 14.936622] softirqs last disabled at (20637): [<ffffffff863683d7>] __irq_exit_rcu+0x67/0xd0
[ 14.936672] ---[ end trace 0000000000000000 ]---
[ 14.953282] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
[ 14.953352] ------------[ cut here ]------------
[ 14.953383] WARNING: CPU: 2 PID: 360 at kernel/sched/ext.c:4335 scx_ops_bypass+0x1d8/0x280
[ 14.953428] Modules linked in:
[ 14.953453] CPU: 2 UID: 0 PID: 360 Comm: sched_ext_ops_h Tainted: G W 6.11.0-virtme #24
[ 14.953505] Tainted: [W]=WARN
[ 14.953527] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
[ 14.953574] RIP: 0010:scx_ops_bypass+0x1d8/0x280
[ 14.953603] Code: c6 05 7b 34 e8 01 01 90 48 c7 c7 89 86 88 87 e8 be 1d f8 ff 90 0f 0b 90 90 eb 95 90 0f 0b 90 41 8b 84 24 24 0a 00 00 eb 97 90 <0f> 0b 90 41 8b 84 24 24 0a 00 00 eb 92 f3 0f 1e fa 49 8d 84 24 f0
[ 14.953693] RSP: 0018:ffffb706c0957ce0 EFLAGS: 00010046
[ 14.953722] RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000001
[ 14.953763] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8fc5fec31318
[ 14.953804] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
[ 14.953845] R10: ffffffff863a9795 R11: 0000000000000000 R12: ffff8fc5fec31300
[ 14.953888] R13: ffff8fc5fec31318 R14: 0000000000000286 R15: 0000000000000018
[ 14.953934] FS: 0000000000000000(0000) GS:ffff8fc5fe680000(0000) knlGS:0000000000000000
[ 14.953974] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 14.954009] CR2: 0000557d92890b88 CR3: 000000002464a000 CR4: 0000000000750ef0
[ 14.954052] PKRU: 55555554
[ 14.954068] Call Trace:
[ 14.954085] <TASK>
[ 14.954102] ? __warn+0xce/0x220
[ 14.954126] ? scx_ops_bypass+0x1d8/0x280
[ 14.954150] ? report_bug+0xc1/0x160
[ 14.954178] ? handle_bug+0x61/0x90
[ 14.954203] ? exc_invalid_op+0x1a/0x50
[ 14.954226] ? asm_exc_invalid_op+0x1a/0x20
[ 14.954250] ? raw_spin_rq_lock_nested+0x15/0x30
[ 14.954285] ? scx_ops_bypass+0x1d8/0x280
[ 14.954311] ? __mutex_unlock_slowpath+0x3a/0x260
[ 14.954343] scx_ops_disable_workfn+0xa3e/0xac0
[ 14.954381] ? __pfx_scx_ops_disable_workfn+0x10/0x10
[ 14.954413] kthread_worker_fn+0x101/0x2c0
[ 14.954442] ? __pfx_kthread_worker_fn+0x10/0x10
[ 14.954479] kthread+0xec/0x110
[ 14.954507] ? __pfx_kthread+0x10/0x10
[ 14.954530] ret_from_fork+0x37/0x50
[ 14.954553] ? __pfx_kthread+0x10/0x10
[ 14.954576] ret_from_fork_asm+0x1a/0x30
[ 14.954603] </TASK>
[ 14.954621] irq event stamp: 21002
[ 14.954644] hardirqs last enabled at (21001): [<ffffffff863aa35f>] resched_cpu+0x9f/0xd0
[ 14.954686] hardirqs last disabled at (21002): [<ffffffff863dd0ba>] scx_ops_bypass+0x11a/0x280
[ 14.954735] softirqs last enabled at (20642): [<ffffffff863683d7>] __irq_exit_rcu+0x67/0xd0
[ 14.954782] softirqs last disabled at (20637): [<ffffffff863683d7>] __irq_exit_rcu+0x67/0xd0
[ 14.954829] ---[ end trace 0000000000000000 ]---
[ 15.022283] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
[ 15.092282] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
[ 15.149282] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
ok 1 exit #
===== END =====
And with it, the test passes without issue after 1000s of runs:
.[root@virtme-ng sched_ext]# ./runner -t exit
===== START =====
TEST: exit
DESCRIPTION: Verify we can cleanly exit a scheduler in multiple places
OUTPUT:
[ 7.412856] sched_ext: BPF scheduler "exit" enabled
[ 7.427924] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
[ 7.466677] sched_ext: BPF scheduler "exit" enabled
[ 7.475923] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
[ 7.512803] sched_ext: BPF scheduler "exit" enabled
[ 7.532924] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
[ 7.586809] sched_ext: BPF scheduler "exit" enabled
[ 7.595926] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
[ 7.661923] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
[ 7.723923] sched_ext: BPF scheduler "exit" disabled (unregistered from BPF)
ok 1 exit #
===== END =====
=============================
RESULTS:
PASSED: 1
SKIPPED: 0
FAILED: 0
Fixes: f0e1a0643a ("sched_ext: Implement BPF extensible scheduler class")
Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
David Vernet
Tejun Heo
parent
895669fd0d
commit
0e7ffff1b8
@ -862,7 +862,8 @@ static DEFINE_MUTEX(scx_ops_enable_mutex);
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DEFINE_STATIC_KEY_FALSE(__scx_ops_enabled);
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DEFINE_STATIC_PERCPU_RWSEM(scx_fork_rwsem);
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static atomic_t scx_ops_enable_state_var = ATOMIC_INIT(SCX_OPS_DISABLED);
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static atomic_t scx_ops_bypass_depth = ATOMIC_INIT(0);
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static int scx_ops_bypass_depth;
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static DEFINE_RAW_SPINLOCK(__scx_ops_bypass_lock);
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static bool scx_ops_init_task_enabled;
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static bool scx_switching_all;
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DEFINE_STATIC_KEY_FALSE(__scx_switched_all);
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@ -4298,18 +4299,20 @@ bool task_should_scx(struct task_struct *p)
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*/
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static void scx_ops_bypass(bool bypass)
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{
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int depth, cpu;
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int cpu;
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unsigned long flags;
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raw_spin_lock_irqsave(&__scx_ops_bypass_lock, flags);
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if (bypass) {
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depth = atomic_inc_return(&scx_ops_bypass_depth);
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WARN_ON_ONCE(depth <= 0);
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if (depth != 1)
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return;
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scx_ops_bypass_depth++;
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WARN_ON_ONCE(scx_ops_bypass_depth <= 0);
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if (scx_ops_bypass_depth != 1)
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goto unlock;
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} else {
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depth = atomic_dec_return(&scx_ops_bypass_depth);
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WARN_ON_ONCE(depth < 0);
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if (depth != 0)
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return;
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scx_ops_bypass_depth--;
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WARN_ON_ONCE(scx_ops_bypass_depth < 0);
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if (scx_ops_bypass_depth != 0)
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goto unlock;
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}
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/*
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@ -4326,7 +4329,7 @@ static void scx_ops_bypass(bool bypass)
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struct rq_flags rf;
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struct task_struct *p, *n;
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rq_lock_irqsave(rq, &rf);
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rq_lock(rq, &rf);
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if (bypass) {
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WARN_ON_ONCE(rq->scx.flags & SCX_RQ_BYPASSING);
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@ -4362,11 +4365,13 @@ static void scx_ops_bypass(bool bypass)
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sched_enq_and_set_task(&ctx);
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}
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rq_unlock_irqrestore(rq, &rf);
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rq_unlock(rq, &rf);
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/* resched to restore ticks and idle state */
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resched_cpu(cpu);
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}
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unlock:
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raw_spin_unlock_irqrestore(&__scx_ops_bypass_lock, flags);
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}
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static void free_exit_info(struct scx_exit_info *ei)
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