[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen: fix xen_qlock_wait()
On 09/11/18 16:20, Juergen Gross wrote: > On 09/11/2018 16:02, Sander Eikelenboom wrote: >> On 09/11/18 13:04, Juergen Gross wrote: >>> Commit a856531951dc80 ("xen: make xen_qlock_wait() nestable") >>> introduced a regression for Xen guests running fully virtualized >>> (HVM or PVH mode). The Xen hypervisor wouldn't return from the poll >>> hypercall with interrupts disabled in case of an interrupt (for PV >>> guests it does). >>> >>> So instead of disabling interrupts in xen_qlock_wait() use a nesting >>> counter to avoid calling xen_clear_irq_pending() in case >>> xen_qlock_wait() is nested. >>> >>> Fixes: a856531951dc80 ("xen: make xen_qlock_wait() nestable") >>> Cc: stable@xxxxxxxxxxxxxxx >>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx> >> >> Although you don't seem too interested, you can stick on a: >> Tested-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx> >> if you like. > > I am interested. > > OTOH I wanted to post the patch officially to give others the chance to > send remarks. OK, would be nice to at least be CC'ed on patches going upstream when you have been reporting stuff. -- Sander > > Juergen > >> >> -- >> Sander >> >>> --- >>> arch/x86/xen/spinlock.c | 14 ++++++++------ >>> 1 file changed, 8 insertions(+), 6 deletions(-) >>> >>> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c >>> index 441c88262169..1c8a8816a402 100644 >>> --- a/arch/x86/xen/spinlock.c >>> +++ b/arch/x86/xen/spinlock.c >>> @@ -9,6 +9,7 @@ >>> #include <linux/log2.h> >>> #include <linux/gfp.h> >>> #include <linux/slab.h> >>> +#include <linux/atomic.h> >>> >>> #include <asm/paravirt.h> >>> #include <asm/qspinlock.h> >>> @@ -21,6 +22,7 @@ >>> >>> static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; >>> static DEFINE_PER_CPU(char *, irq_name); >>> +static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest); >>> static bool xen_pvspin = true; >>> >>> static void xen_qlock_kick(int cpu) >>> @@ -39,25 +41,25 @@ 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); >>> + atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest); >>> >>> /* If kicker interrupts not initialized yet, just spin */ >>> if (irq == -1 || in_nmi()) >>> return; >>> >>> - /* Guard against reentry. */ >>> - local_irq_save(flags); >>> + /* Detect reentry. */ >>> + atomic_inc(nest_cnt); >>> >>> - /* If irq pending already clear it. */ >>> - if (xen_test_irq_pending(irq)) { >>> + /* If irq pending already and no nested call clear it. */ >>> + if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) { >>> xen_clear_irq_pending(irq); >>> } else if (READ_ONCE(*byte) == val) { >>> /* Block until irq becomes pending (or a spurious wakeup) */ >>> xen_poll_irq(irq); >>> } >>> >>> - local_irq_restore(flags); >>> + atomic_dec(nest_cnt); >>> } >>> >>> 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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