From: John Ogness <[email protected]> Sent: Tuesday, January 26, 2021 1:16 PM > > In preparation for removing printk's @logbuf_lock, dumpers that have > assumed to be protected against parallel calls must provide their own > synchronization. Add a locally static spinlock to synchronize the > kmsg_dump call. > > Signed-off-by: John Ogness <[email protected]> > --- > drivers/hv/vmbus_drv.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c > index fbeddef90941..08db95e1a139 100644 > --- a/drivers/hv/vmbus_drv.c > +++ b/drivers/hv/vmbus_drv.c > @@ -1362,23 +1362,27 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper, > enum kmsg_dump_reason reason, > struct kmsg_dumper_iter *iter) > { > + static DEFINE_SPINLOCK(lock); > size_t bytes_written; > phys_addr_t panic_pa; > + unsigned long flags; > > /* We are only interested in panics. */ > if ((reason != KMSG_DUMP_PANIC) || (!sysctl_record_panic_msg)) > return; > > + if (!spin_trylock_irqsave(&lock, flags)) > + return; > + > panic_pa = virt_to_phys(hv_panic_page); > > - /* > - * Write dump contents to the page. No need to synchronize; panic should > - * be single-threaded. > - */ > + /* Write dump contents to the page. */ > kmsg_dump_get_buffer(iter, false, hv_panic_page, HV_HYP_PAGE_SIZE, > &bytes_written); > if (bytes_written) > hyperv_report_panic_msg(panic_pa, bytes_written); > + > + spin_unlock_irqrestore(&lock, flags); > } > > static struct kmsg_dumper hv_kmsg_dumper = { > -- > 2.20.1
I don't think this patch is needed. Per some of the unmodified code above, and the comment, we proceed to the call to kmsg_dump_get_buffer() only in the panic path. Code in the panic path prior to invoking kmsg_dump() ensures that we are single-threaded on a single CPU. So I think everything is good here without the new spin lock. The subsequent call to hyperv_report_panic_msg() also assumes that we are single-threaded. Michael
