I do not see a straightforward backport of this patch without pulling more changes in. Do we have anybody to actually hit the issue on those older kernels? While the issue is possible in principle I do not remember anybody complaining. On Mon 14-01-19 15:57:16, Greg KH wrote: > >From 63f3655f950186752236bb88a22f8252c11ce394 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@xxxxxxxx> > Date: Tue, 8 Jan 2019 15:23:07 -0800 > Subject: [PATCH] mm, memcg: fix reclaim deadlock with writeback > > Liu Bo has experienced a deadlock between memcg (legacy) reclaim and the > ext4 writeback > > task1: > wait_on_page_bit+0x82/0xa0 > shrink_page_list+0x907/0x960 > shrink_inactive_list+0x2c7/0x680 > shrink_node_memcg+0x404/0x830 > shrink_node+0xd8/0x300 > do_try_to_free_pages+0x10d/0x330 > try_to_free_mem_cgroup_pages+0xd5/0x1b0 > try_charge+0x14d/0x720 > memcg_kmem_charge_memcg+0x3c/0xa0 > memcg_kmem_charge+0x7e/0xd0 > __alloc_pages_nodemask+0x178/0x260 > alloc_pages_current+0x95/0x140 > pte_alloc_one+0x17/0x40 > __pte_alloc+0x1e/0x110 > alloc_set_pte+0x5fe/0xc20 > do_fault+0x103/0x970 > handle_mm_fault+0x61e/0xd10 > __do_page_fault+0x252/0x4d0 > do_page_fault+0x30/0x80 > page_fault+0x28/0x30 > > task2: > __lock_page+0x86/0xa0 > mpage_prepare_extent_to_map+0x2e7/0x310 [ext4] > ext4_writepages+0x479/0xd60 > do_writepages+0x1e/0x30 > __writeback_single_inode+0x45/0x320 > writeback_sb_inodes+0x272/0x600 > __writeback_inodes_wb+0x92/0xc0 > wb_writeback+0x268/0x300 > wb_workfn+0xb4/0x390 > process_one_work+0x189/0x420 > worker_thread+0x4e/0x4b0 > kthread+0xe6/0x100 > ret_from_fork+0x41/0x50 > > He adds > "task1 is waiting for the PageWriteback bit of the page that task2 has > collected in mpd->io_submit->io_bio, and tasks2 is waiting for the > LOCKED bit the page which tasks1 has locked" > > More precisely task1 is handling a page fault and it has a page locked > while it charges a new page table to a memcg. That in turn hits a > memory limit reclaim and the memcg reclaim for legacy controller is > waiting on the writeback but that is never going to finish because the > writeback itself is waiting for the page locked in the #PF path. So > this is essentially ABBA deadlock: > > lock_page(A) > SetPageWriteback(A) > unlock_page(A) > lock_page(B) > lock_page(B) > pte_alloc_pne > shrink_page_list > wait_on_page_writeback(A) > SetPageWriteback(B) > unlock_page(B) > > # flush A, B to clear the writeback > > This accumulating of more pages to flush is used by several filesystems > to generate a more optimal IO patterns. > > Waiting for the writeback in legacy memcg controller is a workaround for > pre-mature OOM killer invocations because there is no dirty IO > throttling available for the controller. There is no easy way around > that unfortunately. Therefore fix this specific issue by pre-allocating > the page table outside of the page lock. We have that handy > infrastructure for that already so simply reuse the fault-around pattern > which already does this. > > There are probably other hidden __GFP_ACCOUNT | GFP_KERNEL allocations > from under a fs page locked but they should be really rare. I am not > aware of a better solution unfortunately. > > [akpm@xxxxxxxxxxxxxxxxxxxx: fix mm/memory.c:__do_fault()] > [akpm@xxxxxxxxxxxxxxxxxxxx: coding-style fixes] > [mhocko@xxxxxxxxxx: enhance comment, per Johannes] > Link: http://lkml.kernel.org/r/20181214084948.GA5624@xxxxxxxxxxxxxx > Link: http://lkml.kernel.org/r/20181213092221.27270-1-mhocko@xxxxxxxxxx > Fixes: c3b94f44fcb0 ("memcg: further prevent OOM with too many dirty pages") > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > Reported-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx> > Debugged-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx> > Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Reviewed-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx> > Cc: Jan Kara <jack@xxxxxxx> > Cc: Dave Chinner <david@xxxxxxxxxxxxx> > Cc: Theodore Ts'o <tytso@xxxxxxx> > Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> > Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > diff --git a/mm/memory.c b/mm/memory.c > index a52663c0612d..5e46836714dc 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2994,6 +2994,28 @@ static vm_fault_t __do_fault(struct vm_fault *vmf) > struct vm_area_struct *vma = vmf->vma; > vm_fault_t ret; > > + /* > + * Preallocate pte before we take page_lock because this might lead to > + * deadlocks for memcg reclaim which waits for pages under writeback: > + * lock_page(A) > + * SetPageWriteback(A) > + * unlock_page(A) > + * lock_page(B) > + * lock_page(B) > + * pte_alloc_pne > + * shrink_page_list > + * wait_on_page_writeback(A) > + * SetPageWriteback(B) > + * unlock_page(B) > + * # flush A, B to clear the writeback > + */ > + if (pmd_none(*vmf->pmd) && !vmf->prealloc_pte) { > + vmf->prealloc_pte = pte_alloc_one(vmf->vma->vm_mm); > + if (!vmf->prealloc_pte) > + return VM_FAULT_OOM; > + smp_wmb(); /* See comment in __pte_alloc() */ > + } > + > ret = vma->vm_ops->fault(vmf); > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY | > VM_FAULT_DONE_COW))) > -- Michal Hocko SUSE Labs
