> -----Original Message----- > From: Andrea Arcangeli [mailto:aarcange@xxxxxxxxxx] > Sent: Wednesday, December 04, 2013 3:51 AM > To: Alexander Graf > Cc: Bhushan Bharat-R65777; linuxppc-dev@xxxxxxxxxxxxxxxx; kvm- > ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; Wood Scott-B07421; Ben Herrenschmidt > Subject: Re: Error in frreing hugepages with preemption enabled > > Hi everyone, > > On Fri, Nov 29, 2013 at 12:13:03PM +0100, Alexander Graf wrote: > > > > On 29.11.2013, at 05:38, Bharat Bhushan <Bharat.Bhushan@xxxxxxxxxxxxx> wrote: > > > > > Hi Alex, > > > > > > I am running KVM guest with host kernel having CONFIG_PREEMPT enabled. With > allocated pages things seems to work fine but I uses hugepages for guest I see > below prints when "quit" from qemu. > > > > > > (qemu) QEMU waiting for connection on: telnet:0.0.0.0:4444,server > > > qemu-system-ppc64: pci_add_option_rom: failed to find romfile "efi- > virtio.rom" > > > q > > > debug_smp_processor_id: 15 callbacks suppressed > > > BUG: using smp_processor_id() in preemptible [00000000] code: > > > qemu-system-ppc/2504 caller is .free_hugepd_range+0xb0/0x21c > > > CPU: 1 PID: 2504 Comm: qemu-system-ppc Not tainted > > > 3.12.0-rc3-07733-gabf4907 #175 Call Trace: > > > [c0000000fb433400] [c000000000007d38] .show_stack+0x7c/0x1cc > > > (unreliable) [c0000000fb4334d0] [c0000000005e8ce0] > > > .dump_stack+0x9c/0xf4 [c0000000fb433560] [c0000000002de5ec] > > > .debug_smp_processor_id+0x108/0x11c > > > [c0000000fb4335f0] [c000000000025e10] .free_hugepd_range+0xb0/0x21c > > > [c0000000fb433680] [c0000000000265bc] > > > .hugetlb_free_pgd_range+0x2c8/0x3b0 > > > [c0000000fb4337a0] [c0000000000e428c] .free_pgtables+0x14c/0x158 > > > [c0000000fb433840] [c0000000000ef320] .exit_mmap+0xec/0x194 > > > [c0000000fb433960] [c00000000004d780] .mmput+0x64/0x124 > > > [c0000000fb4339e0] [c000000000051f40] .do_exit+0x29c/0x9c8 > > > [c0000000fb433ae0] [c0000000000527c8] .do_group_exit+0x50/0xc4 > > > [c0000000fb433b70] [c0000000000606a0] > > > .get_signal_to_deliver+0x21c/0x5d8 > > > [c0000000fb433c70] [c000000000009b08] .do_signal+0x54/0x278 > > > [c0000000fb433db0] [c000000000009e50] .do_notify_resume+0x64/0x78 > > > [c0000000fb433e30] [c000000000000b44] > > > .ret_from_except_lite+0x70/0x74 > > > > > > > > > This mean that free_hugepd_range() must be called with preemption enabled. > > > > with preemption disabled. > > > > > I tried below change and this seems to work fine (I am not having > > > expertise in this area so not sure this is correct way) > > > > Not sure - the scope looks odd to me. Let's ask Andrea - I'm sure he knows > what to do :). > > :) So I had a look at the top of this function (0xb0) in the upstream kernel and > no smp_processor_id() call is apparent, is this stock git or a ppc tree? The > first few calls seem not to call it but I may have overlooked something. It's > just quicker if somebody with vmlinux finds the location of it. > > static void free_hugepd_range(struct mmu_gather *tlb, hugepd_t *hpdp, int > pdshift, > unsigned long start, unsigned long end, > unsigned long floor, unsigned long ceiling) { > pte_t *hugepte = hugepd_page(*hpdp); > int i; > > unsigned long pdmask = ~((1UL << pdshift) - 1); > unsigned int num_hugepd = 1; > > #ifdef CONFIG_PPC_FSL_BOOK3E > /* Note: On fsl the hpdp may be the first of several */ > num_hugepd = (1 << (hugepd_shift(*hpdp) - pdshift)); #else > unsigned int shift = hugepd_shift(*hpdp); #endif > > start &= pdmask; > if (start < floor) > return; > if (ceiling) { > ceiling &= pdmask; > if (! ceiling) > return; > } > if (end - 1 > ceiling - 1) > return; > > for (i = 0; i < num_hugepd; i++, hpdp++) > hpdp->pd = 0; > > tlb->need_flush = 1; > > #ifdef CONFIG_PPC_FSL_BOOK3E > hugepd_free(tlb, hugepte); > #else > pgtable_free_tlb(tlb, hugepte, pdshift - shift); #endif } > > Generally smp_processor_id should never be used, exactly to avoid problems like > above with preempion enabled in .config. > > Instead it should be replaced with a get_cpu()/put_cpu() pair that is exactly > meant to fix bugs like this and define proper critical sections around the per- > cpu variables. > > #define get_cpu() ({ preempt_disable(); smp_processor_id(); }) > #define put_cpu() preempt_enable() > > After you find where that smp_processor_id() is located, you should simply > replace it with a get_cpu() and then you should insert a put_cpu immediately > after the "cpu" info is not used anymore. That will define a proper and strict > critical section around the use of the per-cpu variables. > > With a ppc vmlinux it should be immediate to find the location of > smp_processor_id but I don't have the ppc vmlinux here. Thanks Andrea for the details description. It is really helpful I will look into this. Thanks -Bharat > > Thanks! > Andrea > > > > > > > Alex > > > > > > > > diff --git a/arch/powerpc/mm/hugetlbpage.c > > > b/arch/powerpc/mm/hugetlbpage.c index d67db4b..6bf8459 100644 > > > --- a/arch/powerpc/mm/hugetlbpage.c > > > +++ b/arch/powerpc/mm/hugetlbpage.c > > > @@ -563,8 +563,10 @@ static void hugetlb_free_pmd_range(struct mmu_gather > *tlb, pud_t *pud, > > > */ > > > next = addr + (1 << hugepd_shift(*(hugepd_t *)pmd)); > > > #endif > > > + preempt_disable(); > > > free_hugepd_range(tlb, (hugepd_t *)pmd, PMD_SHIFT, > > > addr, next, floor, ceiling); > > > + preempt_enable(); > > > } while (addr = next, addr != end); > > > > > > start &= PUD_MASK; > > > > > > > > > Thanks > > > -Bharat > > > > > > -- > > > To unsubscribe from this list: send the line "unsubscribe kvm-ppc" > > > in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo > > > info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
