Messages in this thread | | | Date | Tue, 19 Jun 2012 12:46:23 -0700 | From | Frank Rowand <> | Subject | Re: [RFC][RT][PATCH] mm: Do not use stop_machine() for __zone_pcp_udpate() for CONFIG_PREEMPT_RT_FULL |
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Adding to the distribution list: the author of the patch that included the call to stop_machine() (commit 112067f0905b2de862c607ee62411cf47d2fe5c4).
On 06/19/12 11:32, Aaditya Kumar wrote: > The code path of __zone_pcp_update() has following locks, which in > CONFIG_PREEMPT_RT_FULL=y are rt-mutex. > - pa_lock locked by cpu_lock_irqsave() > - zone->lock locked by free_pcppages_bulk() > > Since __zone_pcp_update() is called from stop_machine(), so with > CONFIG_PREEMPT_RT_FULL=y > we get following backtrace when __zone_pcp_update() is called during > memory hot plugging while > doing heavy file I/O. > > I think stop_machine() may not be required for calling __zone_pcp_update() > in case of CONFIG_PREEMPT_RT_FULL=y as acquiring pa_lock in __zone_pcp_update() > should be sufficient to isolate pcp pages and to setup per cpu pagesets. > > Can someone please let me know if am missing anything here? > > > The backtrace that this patch fixes: > BUG: scheduling while atomic: migration/0/7/0x00000002 > Modules linked in: v2p > Backtrace: > [<800111a0>] (dump_backtrace+0x0/0x10c) from [<802d7b7c>] > (dump_stack+0x18/0x1c) > r6:80c8fc28 r5:80c8f9a0 r4:00000000 r3:60000013 > [<802d7b64>] (dump_stack+0x0/0x1c) from [<8001e81c>] (__schedule_bug+0x64/0x74) > [<8001e7b8>] (__schedule_bug+0x0/0x74) from [<802d7fa0>] > (__schedule+0x68/0x604) > r4:8051bf00 r3:00000000 > [<802d7f38>] (__schedule+0x0/0x604) from [<802d8a78>] (schedule+0x98/0xbc) > [<802d89e0>] (schedule+0x0/0xbc) from [<802d9e14>] > (rt_spin_lock_slowlock+0x168/0x240) > r4:805228f4 r3:00000000 > [<802d9cac>] (rt_spin_lock_slowlock+0x0/0x240) from [<802da234>] > (rt_spin_lock+0x10/0x14) > [<802da224>] (rt_spin_lock+0x0/0x14) from [<8008694c>] > (__zone_pcp_update+0x58/0xd8) > [<800868f4>] (__zone_pcp_update+0x0/0xd8) from [<800603ec>] > (stop_machine_cpu_stop+0xb0/0x104) > [<8006033c>] (stop_machine_cpu_stop+0x0/0x104) from [<80060200>] > (cpu_stopper_thread+0xd4/0x188) > > > Signed-off-by: Aaditya Kumar <aaditya.kumar@ap.sony.com> > > --- > mm/page_alloc.c | 4 4 + 0 - 0 ! > 1 file changed, 4 insertions(+) > > Index: b/mm/page_alloc.c > =================================================================== > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3868,7 +3868,11 @@ static int __zone_pcp_update(void *data) > > void zone_pcp_update(struct zone *zone) > { > +#ifndef CONFIG_PREEMPT_RT_FULL > stop_machine(__zone_pcp_update, zone, NULL); > +#else > + __zone_pcp_update(zone); > +#endif > } > > static __meminit void zone_pcp_init(struct zone *zone) > > . >
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