From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from jenni1.inet.fi (mta-out.inet.fi [195.156.147.13]) by ozlabs.org (Postfix) with ESMTP id BE0CC2C00A1 for ; Thu, 2 Jan 2014 13:26:37 +1100 (EST) Date: Thu, 2 Jan 2014 04:19:51 +0200 From: "Kirill A. Shutemov" To: Benjamin Herrenschmidt , "Aneesh Kumar K.V" Subject: Re: [PATCH] powerpc: thp: Fix crash on mremap Message-ID: <20140102021951.GA26369@node.dhcp.inet.fi> References: <1388570027-22933-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1388572145.4373.41.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1388572145.4373.41.camel@pasglop> Cc: aarcange@redhat.com, linuxppc-dev@lists.ozlabs.org, paulus@samba.org, kirill.shutemov@linux.intel.com, linux-mm@kvack.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Jan 01, 2014 at 09:29:05PM +1100, Benjamin Herrenschmidt wrote: > On Wed, 2014-01-01 at 15:23 +0530, Aneesh Kumar K.V wrote: > > From: "Aneesh Kumar K.V" > > > > This patch fix the below crash > > > > NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440 > > LR [c0000000000439ac] .hash_page+0x18c/0x5e0 > > ... > > Call Trace: > > [c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable) > > [437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0 > > [437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58 > > > > On ppc64 we use the pgtable for storing the hpte slot information and > > store address to the pgtable at a constant offset (PTRS_PER_PMD) from > > pmd. On mremap, when we switch the pmd, we need to withdraw and deposit > > the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset > > from new pmd. > > > > We also want to move the withdraw and deposit before the set_pmd so > > that, when page fault find the pmd as trans huge we can be sure that > > pgtable can be located at the offset. > > > > Signed-off-by: Aneesh Kumar K.V > > --- > > NOTE: > > For other archs we would just be removing the pgtable from the list and adding it back. > > I didn't find an easy way to make it not do that without lots of #ifdef around. Any > > suggestion around that is welcome. > > What about > > - if (new_ptl != old_ptl) { > + if (new_ptl != old_ptl || ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW) { > > Or something similar ? Looks sane to me. Or something with IS_ENABLED(), if needed. > > Cheers, > Ben. > > > mm/huge_memory.c | 21 ++++++++++----------- > > 1 file changed, 10 insertions(+), 11 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 7de1bf85f683..eb2e60d9ba45 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -1500,24 +1500,23 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma, > > */ > > ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl); > > if (ret == 1) { > > + pgtable_t pgtable; > > + > > new_ptl = pmd_lockptr(mm, new_pmd); > > if (new_ptl != old_ptl) > > spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); > > pmd = pmdp_get_and_clear(mm, old_addr, old_pmd); > > VM_BUG_ON(!pmd_none(*new_pmd)); > > + /* > > + * Archs like ppc64 use pgtable to store per pmd > > + * specific information. So when we switch the pmd, > > + * we should also withdraw and deposit the pgtable > > + */ > > + pgtable = pgtable_trans_huge_withdraw(mm, old_pmd); > > + pgtable_trans_huge_deposit(mm, new_pmd, pgtable); > > set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd)); > > - if (new_ptl != old_ptl) { > > - pgtable_t pgtable; > > - > > - /* > > - * Move preallocated PTE page table if new_pmd is on > > - * different PMD page table. > > - */ Please don't lose the comment. > > - pgtable = pgtable_trans_huge_withdraw(mm, old_pmd); > > - pgtable_trans_huge_deposit(mm, new_pmd, pgtable); > > - > > + if (new_ptl != old_ptl) > > spin_unlock(new_ptl); > > - } > > spin_unlock(old_ptl); > > } > > out: > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Kirill A. Shutemov