On Tue, 20 Apr 2010 12:58:43 +0900 Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > On Tue, Apr 20, 2010 at 12:07 PM, KAMEZAWA Hiroyuki > <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > On Tue, 20 Apr 2010 11:39:46 +0900 > >> Dumb question. Why can't we call arch_alloc_page and kernel_map_pages > >> as interrupt disabled? It's deadlock issue or latency issue? > >> I don't found any comment about it. > >> It should have added the comment around that functions. :) > >> > > > > I guess it's from the same reason as vfree(), which can't be called under > > irq-disabled. > > > > Both of them has to flush TLB of all cpus. At flushing TLB (of other cpus), cpus has > > to send IPI via smp_call_function. What I know from old stories is below. > > > > At sendinf IPI, usual sequence is following. (This may be old.) > > > > spin_lock(&ipi_lock); > > set up cpu mask for getting notification from other cpu for declearing > > "I received IPI and finished my own work". > > spin_unlock(&ipi_lock); > > > > Then, > > CPU0 CPU1 > > > > irq_disable (somewhere) spin_lock > > send IPI and wait for notification. > > spin_lock() > > > > deadlock. Seeing decription of kernel/smp.c::smp_call_function_many(), it says > > this function should not be called under irq-disabled. > > (Maybe the same kind of spin-wait deadlock can happen.) > > > > Thanks for kind explanation. > Actually I guessed TLB issue but I can't find any glue point which > connect tlb flush to smp_call_function_xxx. :( > > Now look at the __native_flush_tlb_global. > It just read and write cr4 with just mask off X86_CR4_PGE. > So i don't know how connect this and smp_schedule_xxxx. > Hmm,, maybe APIC? > > Sorry for dumb question. > Hmm...seeing again, arch/x86/mm/pageattr.c::kernel_map_pages() says: 1293 /* 1294 * We should perform an IPI and flush all tlbs, 1295 * but that can deadlock->flush only current cpu: 1296 */ Wow. It just flush only local cpu. Then, no IPI. Hmm...all other archs does the same thing ? If so, kernel_map_pages() can be called under irq_disabled. The author of kernel_map_pages() is aware that this can be called under irq-disabled. Hmm... Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>