Message-ID: <20220728003401.7fmppx5kbfqmzyjb@revolver>
Date:   Thu, 28 Jul 2022 00:34:07 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Nathan Chancellor <nathan@...nel.org>
CC:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>
Subject: Re: [PATCH v12 08/69] mm: start tracking VMAs with maple tree

* Nathan Chancellor <nathan@...nel.org> [220726 20:28]:
> Hi Liam,
> 
> On Wed, Jul 20, 2022 at 02:17:45AM +0000, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> > 
> > Start tracking the VMAs with the new maple tree structure in parallel with
> > the rb_tree.  Add debug and trace events for maple tree operations and
> > duplicate the rb_tree that is created on forks into the maple tree.
> > 
> > The maple tree is added to the mm_struct including the mm_init struct,
> > added support in required mm/mmap functions, added tracking in kernel/fork
> > for process forking, and used to find the unmapped_area and checked
> > against what the rbtree finds.
> > 
> > This also moves the mmap_lock() in exit_mmap() since the oom reaper call
> > does walk the VMAs.  Otherwise lockdep will be unhappy if oom happens.
> > 
> > When splitting a vma fails due to allocations of the maple tree nodes,
> > the error path in __split_vma() calls new->vm_ops->close(new).  The page
> > accounting for hugetlb is actually in the close() operation,  so it
> > accounts for the removal of 1/2 of the VMA which was not adjusted.  This
> > results in a negative exit value.  To avoid the negative charge, set
> > vm_start = vm_end and vm_pgoff = 0.
> > 
> > There is also a potential accounting issue in special mappings from
> > insert_vm_struct() failing to allocate, so reverse the charge there in
> > the failure scenario.
> > 
> > Link: https://lkml.kernel.org/r/20220504010716.661115-10-Liam.Howlett@oracle.com
> > Link: https://lkml.kernel.org/r/20220621204632.3370049-9-Liam.Howlett@oracle.com
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: David Howells <dhowells@...hat.com>
> > Cc: SeongJae Park <sj@...nel.org>
> > Cc: Vlastimil Babka <vbabka@...e.cz>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Davidlohr Bueso <dave@...olabs.net>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> 
> Apologies if this has been reported already, I tried searching the
> mailing lists but I did not really find anything.
> 
> I bisected my arm64 test system failing to boot to this change as commit
> fdfbd22f37db ("mm: start tracking VMAs with maple tree") in
> next-20220726 (bisect log at the end).
> 
> [    4.295886] Unable to handle kernel access to user memory outside uaccess routines at virtual address 0000000000000000
> [    4.306595] Mem abort info:
> [    4.309381]   ESR = 0x0000000096000044
> [    4.313118]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    4.318422]   SET = 0, FnV = 0
> [    4.321464]   EA = 0, S1PTW = 0
> [    4.324592]   FSC = 0x04: level 0 translation fault
> [    4.329461] Data abort info:
> [    4.332329]   ISV = 0, ISS = 0x00000044
> [    4.336152]   CM = 0, WnR = 1
> [    4.339110] user pgtable: 4k pages, 48-bit VAs, pgdp=00000020a9712000
> [    4.345539] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
> [    4.352321] Internal error: Oops: 96000044 [#1] SMP
> [    4.357188] Modules linked in:
> [    4.360232] CPU: 6 PID: 264 Comm: dracut-rootfs-g Not tainted 5.19.0-rc4-00288-gfdfbd22f37db #1
> [    4.368918] Hardware name: SolidRun Ltd. SolidRun CEX7 Platform, BIOS EDK II Jun 21 2022
> [    4.376994] pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [    4.383943] pc : mas_split.isra.0+0x50c/0x784
> [    4.388295] lr : mas_split.isra.0+0x204/0x784
> [    4.392640] sp : ffff8000094a3510
> [    4.395942] x29: ffff8000094a3510 x28: ffff08dd66c0c000 x27: ffff8000094a3610
> [    4.403067] x26: ffff8000094a35d0 x25: ffff8000094a3578 x24: ffffd823cb5448b8
> [    4.410192] x23: ffff8000094a3650 x22: ffff8000094a3690 x21: ffff8000094a3738
> [    4.417316] x20: 0000000000000002 x19: ffff8000094a3af0 x18: 0000000000000002
> [    4.424441] x17: 0000000000000000 x16: ffff08dd66c45450 x15: 0000000000000000
> [    4.431565] x14: ffff08dd66c459c8 x13: ffff8000094a3748 x12: 0000000000000001
> [    4.438689] x11: ffff8000094a3610 x10: 0000000000000003 x9 : ffff08dd66c47300
> [    4.445813] x8 : 000000000000001c x7 : 0000000000000003 x6 : 0000000000000006
> [    4.452937] x5 : ffff08dd68a44409 x4 : 0000000000000001 x3 : ffff8000094a35d0
> [    4.460061] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff8000094a3738
> [    4.467186] Call trace:
> [    4.469620]  mas_split.isra.0+0x50c/0x784
> [    4.473618]  mas_commit_b_node.isra.0+0x1e0/0x274
> [    4.478311]  mas_wr_modify+0x10c/0x28c
> [    4.482048]  mas_wr_store_entry.isra.0+0x10c/0x4a0
> [    4.486827]  mas_store+0x48/0x110
> [    4.490131]  dup_mmap+0x268/0x514
> [    4.493436]  dup_mm+0x68/0xfc
> [    4.496391]  copy_process+0x864/0x10b4
> [    4.500129]  kernel_clone+0x88/0x494
> [    4.503692]  __do_sys_clone+0x60/0x80
> [    4.507342]  __arm64_sys_clone+0x2c/0x40
> [    4.511254]  invoke_syscall+0x78/0x100
> [    4.514991]  el0_svc_common.constprop.0+0x4c/0xf4
> [    4.519683]  do_el0_svc+0x38/0x4c
> [    4.522985]  el0_svc+0x34/0x100
> [    4.526115]  el0t_64_sync_handler+0x11c/0x150
> [    4.530460]  el0t_64_sync+0x190/0x194
> [    4.534112] Code: f9000125 f9400e65 9278dca5 f94000a5 (f9000045)
> [    4.540193] ---[ end trace 0000000000000000 ]---
> 
> I was also able to reproduce the same crash in a Fedora virtual machine
> using QEMU with Fedora's rawhide configuration [1]:
> 
> [    5.913992] Unable to handle kernel access to user memory outside uaccess routines at virtual address 0000000000000000
> [    5.914510] Mem abort info:
> [    5.914581]   ESR = 0x0000000096000044
> [    5.914705]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    5.914858]   SET = 0, FnV = 0
> [    5.914951]   EA = 0, S1PTW = 0
> [    5.915065]   FSC = 0x04: level 0 translation fault
> [    5.915215] Data abort info:
> [    5.915321]   ISV = 0, ISS = 0x00000044
> [    5.915465]   CM = 0, WnR = 1
> [    5.915624] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000103051000
> [    5.915799] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
> [    5.916196] Internal error: Oops: 96000044 [#1] SMP
> [    5.916504] Modules linked in:
> [    5.916771] CPU: 2 PID: 202 Comm: dracut-rootfs-g Not tainted 5.19.0-rc4+ #1
> [    5.917003] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
> [    5.917339] pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [    5.917584] pc : mas_split.isra.0+0x50c/0x784
> [    5.917794] lr : mas_split.isra.0+0x204/0x784
> [    5.917949] sp : ffff8000086334a0
> [    5.918038] x29: ffff8000086334a0 x28: ffff5b65c095a258 x27: ffff8000086335a0
> [    5.918289] x26: ffff800008633560 x25: ffff800008633508 x24: ffffdb30c80d9778
> [    5.918844] x23: ffff8000086335e0 x22: ffff800008633620 x21: ffff8000086336c8
> [    5.919277] x20: 0000000000000002 x19: ffff800008633a80 x18: 0000000000000002
> [    5.919533] x17: 0000000000000000 x16: ffff5b65c095a4b0 x15: 0000000000000000
> [    5.919747] x14: ffff5b65c095a898 x13: ffff8000086336d8 x12: 0000000000000001
> [    5.919971] x11: ffff8000086335a0 x10: 0000000000000003 x9 : ffff5b66f42e2a00
> [    5.920214] x8 : 000000000000001c x7 : 0000000000000003 x6 : 0000000000000006
> [    5.920493] x5 : ffff5b65c3077309 x4 : 0000000000000001 x3 : ffff800008633560
> [    5.920739] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff8000086336c8
> [    5.921051] Call trace:
> [    5.921152]  mas_split.isra.0+0x50c/0x784
> [    5.921303]  mas_commit_b_node.isra.0+0x1e0/0x274
> [    5.921459]  mas_wr_modify+0x10c/0x28c
> [    5.921565]  mas_wr_store_entry.isra.0+0x10c/0x4a0
> [    5.921725]  mas_store+0x48/0x110
> [    5.921864]  dup_mmap+0x268/0x514
> [    5.921993]  dup_mm+0x68/0xfc
> [    5.922074]  copy_process+0x864/0x10b4
> [    5.922213]  kernel_clone+0x88/0x494
> [    5.922315]  __do_sys_clone+0x60/0x80
> [    5.922444]  __arm64_sys_clone+0x2c/0x40
> [    5.922576]  invoke_syscall+0x78/0x100
> [    5.922686]  el0_svc_common.constprop.0+0x4c/0xf4
> [    5.922847]  do_el0_svc+0x38/0x4c
> [    5.922947]  el0_svc+0x34/0x100
> [    5.923056]  el0t_64_sync_handler+0x11c/0x150
> [    5.923179]  el0t_64_sync+0x190/0x194
> [    5.923365] Code: f9000125 f9400e65 9278dca5 f94000a5 (f9000045)
> [    5.923833] ---[ end trace 0000000000000000 ]---
> 
> If there is any additional information I can provide or patches I can
> test, please let me know!
> 

Hello Nathan,

Thanks for testing this and your report.  You are the first and only
report of this failure so I very much appreciate it.

I run a number of tests on arm64 so I will have to try your kernel
config.  Thanks for including the link.

Regards,
Liam

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