> -----Original Message----- > From: devel [mailto:driverdev-devel-bounces@xxxxxxxxxxxxxxxxxxxxxx] On Behalf > Of Dexuan Cui > Sent: Thursday, July 30, 2015 18:18 > To: David Miller <davem@xxxxxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx> > Cc: olaf@xxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; jasowang@xxxxxxxxxx; > driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > stephen@xxxxxxxxxxxxxxxxxx; stefanha@xxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; > apw@xxxxxxxxxxxxx; pebolle@xxxxxxxxxx; dan.carpenter@xxxxxxxxxx > Subject: RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when > hvsock's callback is running > > > From: David Miller > > Sent: Thursday, July 30, 2015 6:28 > > > From: Dexuan Cui <decui@xxxxxxxxxxxxx> > > > Date: Tue, 28 Jul 2015 05:35:30 -0700 > > > > > > In the SMP guest case, when the per-channel callback hvsock_events() is > > > running on virtual CPU A, if the guest tries to close the connection on > > > virtual CPU B: we invoke vmbus_close() -> vmbus_close_internal(), > > > then we can have trouble: on B, vmbus_close_internal() will send IPI > > > reset_channel_cb() to A, trying to set channel->onchannel_callbackto NULL; > > > on A, if the IPI handler happens between > > > "if (channel->onchannel_callback != NULL)" and invoking > > > channel->onchannel_callback, we'll invoke a function pointer of NULL. > > > > > > This is why the patch is necessary. > > > > > Sorry, I do not accept that you must use conditional locking and/or > > IRQ disabling. > > > > Boil it down to what is necessary for the least common denominator, > > and use that unconditionally. > > Hi David, > Thanks for the comment! > > I agree with you it's not clean to use conditional IRQ disabling. > > Here I didn't use unconditionally IRQ disabling because the Hyper-V netvsc > and storvsc driver's vmbus event callbacks (i.e. netvsc_channel_cb() and > storvsc_on_channel_callback()) may take relatively long time (e.g., netvsc can > operate at a speed of 10Gb) and I think it's bad to disable IRQ for long time > when the callbacks are running in a tasklet context, e.g., the Hyper-V timer > can be affected: see vmbus_isr() -> hv_process_timer_expiration(). > > To resolve the race condition between vmbus_close_internal() and > process_chn_event() in SMP case, now I propose a new method: > > we can serialize the 2 paths by adding > tasklet_disable(hv_context.event_dpc[channel->target_cpu]) and > tasklet_enable(...) in vmbus_close_internal(). > > In this way, we need the least change and we can drop this patch. > > Please let me know your opinion. > > -- Dexuan Hi David, KY and all, May I know your opinion about my idea of adding tasklet_disable/enbable() in vmbus_close_internal() and dropping this patch? Thanks, -- Dexuan _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
