lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 11 Nov 2016 17:37:03 -0800 (PST) From: Hugh Dickins <hughd@...gle.com> To: "Kirill A. Shutemov" <kirill@...temov.name> cc: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>, Hugh Dickins <hughd@...gle.com>, akpm@...ux-foundation.org, benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au, linux-mm@...ck.org, linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org Subject: Re: [PATCH 2/2] mm: THP page cache support for ppc64 On Fri, 11 Nov 2016, Kirill A. Shutemov wrote: > On Fri, Nov 11, 2016 at 05:42:11PM +0530, Aneesh Kumar K.V wrote: > > > > doing this in do_set_pmd keeps this closer to where we set the pmd. Any > > reason you thing we should move it higher up the stack. We already do > > pte_alloc() at the same level for a non transhuge case in > > alloc_set_pte(). > > I vaguely remember Hugh mentioned deadlock of allocation under page-lock vs. > OOM-killer (or something else?). You remember well. It was indeed the OOM killer, but in particular due to the way it used to wait for a current victim to exit, and that exit could be delayed forever by the way munlock_vma_pages_all() goes to lock each page in a VM_LOCKED area - a pity if one of them is the page we hold locked while servicing a fault and need to allocate a pagetable. > > If the deadlock is still there it would be matter of making preallocation > unconditional to fix the issue. I think enough has changed at the OOM killer end that the deadlock is no longer there. I haven't kept up with all the changes made recently, but I think we no longer wait for a unique victim to exit before trying another (reaped mms set MMF_OOM_SKIP); and the OOM reaper skips over VM_LOCKED areas to avoid just such a deadlock. It's still silly that munlock_vma_pages_all() should require page lock on each of those pages; but neither Michal nor I have had time to revisit our attempts to relieve that requirement - mlock.c is not easy. > > But what you propose about doesn't make situation any worse. I'm fine with > that. Yes, I think that's right: if there is a problem, then it would already be problem since alloc_set_pte() was created; but we've seen no reports. Hugh
Powered by blists - more mailing lists