[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/2] xen: make xen_qlock_wait() nestable
Correcting Waiman's mail address On 01/10/2018 09:16, Juergen Gross wrote: > 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@xxxxxxxxxxxxxxx > Cc: longman@xxxxxxxxxx > Cc: peterz@xxxxxxxxxxxxx > Signed-off-by: Juergen Gross <jgross@xxxxxxxx> > --- > arch/x86/xen/spinlock.c | 24 ++++++++++-------------- > 1 file changed, 10 insertions(+), 14 deletions(-) > > diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c > index cd210a4ba7b1..e8d880e98057 100644 > --- a/arch/x86/xen/spinlock.c > +++ b/arch/x86/xen/spinlock.c > @@ -39,29 +39,25 @@ static void xen_qlock_kick(int cpu) > */ > static void xen_qlock_wait(u8 *byte, u8 val) > { > + unsigned long flags; > int irq = __this_cpu_read(lock_kicker_irq); > > /* If kicker interrupts not initialized yet, just spin */ > - if (irq == -1) > + if (irq == -1 || in_nmi()) > return; > > - /* If irq pending already clear it and return. */ > + /* Guard against reentry. */ > + local_irq_save(flags); > + > + /* If irq pending already clear it. */ > if (xen_test_irq_pending(irq)) { > xen_clear_irq_pending(irq); > - return; > + } else if (READ_ONCE(*byte) == val) { > + /* Block until irq becomes pending (or a spurious wakeup) */ > + xen_poll_irq(irq); > } > > - if (READ_ONCE(*byte) != val) > - return; > - > - /* > - * If an interrupt happens here, it will leave the wakeup irq > - * pending, which will cause xen_poll_irq() to return > - * immediately. > - */ > - > - /* Block until irq becomes pending (or perhaps a spurious wakeup) */ > - xen_poll_irq(irq); > + local_irq_restore(flags); > } > > static irqreturn_t dummy_handler(int irq, void *dev_id) > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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