forked from Minki/linux
a856531951
xen_qlock_wait() isn't safe for nested calls due to interrupts. A call
of xen_qlock_kick() might be ignored in case a deeper nesting level
was active right before the call of xen_poll_irq():
CPU 1: CPU 2:
spin_lock(lock1)
spin_lock(lock1)
-> xen_qlock_wait()
-> xen_clear_irq_pending()
Interrupt happens
spin_unlock(lock1)
-> xen_qlock_kick(CPU 2)
spin_lock_irqsave(lock2)
spin_lock_irqsave(lock2)
-> xen_qlock_wait()
-> xen_clear_irq_pending()
clears kick for lock1
-> xen_poll_irq()
spin_unlock_irq_restore(lock2)
-> xen_qlock_kick(CPU 2)
wakes up
spin_unlock_irq_restore(lock2)
IRET
resumes in xen_qlock_wait()
-> xen_poll_irq()
never wakes up
The solution is to disable interrupts in xen_qlock_wait() and not to
poll for the irq in case xen_qlock_wait() is called in nmi context.
Cc: stable@vger.kernel.org
Cc: Waiman.Long@hp.com
Cc: peterz@infradead.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
150 lines
3.5 KiB
C
150 lines
3.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Split spinlock implementation out into its own file, so it can be
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* compiled in a FTRACE-compatible way.
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*/
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#include <linux/kernel_stat.h>
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#include <linux/spinlock.h>
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#include <linux/debugfs.h>
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#include <linux/log2.h>
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#include <linux/gfp.h>
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#include <linux/slab.h>
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#include <asm/paravirt.h>
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#include <asm/qspinlock.h>
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#include <xen/interface/xen.h>
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#include <xen/events.h>
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#include "xen-ops.h"
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#include "debugfs.h"
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static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
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static DEFINE_PER_CPU(char *, irq_name);
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static bool xen_pvspin = true;
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static void xen_qlock_kick(int cpu)
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{
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int irq = per_cpu(lock_kicker_irq, cpu);
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/* Don't kick if the target's kicker interrupt is not initialized. */
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if (irq == -1)
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return;
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xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
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}
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/*
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* Halt the current CPU & release it back to the host
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*/
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static void xen_qlock_wait(u8 *byte, u8 val)
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{
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unsigned long flags;
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int irq = __this_cpu_read(lock_kicker_irq);
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/* If kicker interrupts not initialized yet, just spin */
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if (irq == -1 || in_nmi())
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return;
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/* Guard against reentry. */
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local_irq_save(flags);
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/* If irq pending already clear it. */
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if (xen_test_irq_pending(irq)) {
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xen_clear_irq_pending(irq);
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} else if (READ_ONCE(*byte) == val) {
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/* Block until irq becomes pending (or a spurious wakeup) */
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xen_poll_irq(irq);
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}
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local_irq_restore(flags);
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}
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static irqreturn_t dummy_handler(int irq, void *dev_id)
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{
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BUG();
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return IRQ_HANDLED;
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}
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void xen_init_lock_cpu(int cpu)
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{
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int irq;
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char *name;
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if (!xen_pvspin) {
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if (cpu == 0)
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static_branch_disable(&virt_spin_lock_key);
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return;
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}
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WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
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cpu, per_cpu(lock_kicker_irq, cpu));
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name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
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irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
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cpu,
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dummy_handler,
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IRQF_PERCPU|IRQF_NOBALANCING,
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name,
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NULL);
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if (irq >= 0) {
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disable_irq(irq); /* make sure it's never delivered */
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per_cpu(lock_kicker_irq, cpu) = irq;
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per_cpu(irq_name, cpu) = name;
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}
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printk("cpu %d spinlock event irq %d\n", cpu, irq);
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}
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void xen_uninit_lock_cpu(int cpu)
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{
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if (!xen_pvspin)
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return;
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unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
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per_cpu(lock_kicker_irq, cpu) = -1;
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kfree(per_cpu(irq_name, cpu));
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per_cpu(irq_name, cpu) = NULL;
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}
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PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
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/*
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* Our init of PV spinlocks is split in two init functions due to us
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* using paravirt patching and jump labels patching and having to do
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* all of this before SMP code is invoked.
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*
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* The paravirt patching needs to be done _before_ the alternative asm code
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* is started, otherwise we would not patch the core kernel code.
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*/
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void __init xen_init_spinlocks(void)
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{
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/* Don't need to use pvqspinlock code if there is only 1 vCPU. */
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if (num_possible_cpus() == 1)
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xen_pvspin = false;
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if (!xen_pvspin) {
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printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
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return;
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}
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printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
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__pv_init_lock_hash();
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pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
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pv_ops.lock.queued_spin_unlock =
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PV_CALLEE_SAVE(__pv_queued_spin_unlock);
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pv_ops.lock.wait = xen_qlock_wait;
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pv_ops.lock.kick = xen_qlock_kick;
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pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
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}
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static __init int xen_parse_nopvspin(char *arg)
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{
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xen_pvspin = false;
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return 0;
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}
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early_param("xen_nopvspin", xen_parse_nopvspin);
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