Re: [PATCH v12 08/69] mm: start tracking VMAs with maple tree

Nathan Chancellor
2022-07-29T17:02:58Z

On Fri, Jul 29, 2022 at 03:41:44PM +0000, Liam Howlett wrote:
> * Liam R. Howlett <Liam.Howlett@Oracle.com> [220727 20:34]:
> > * Nathan Chancellor <nathan@kernel.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@Oracle.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@Oracle.com>
> > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > > > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > > > Cc: David Howells <dhowells@redhat.com>
> > > > Cc: SeongJae Park <sj@kernel.org>
> > > > Cc: Vlastimil Babka <vbabka@suse.cz>
> > > > Cc: Will Deacon <will@kernel.org>
> > > > Cc: Davidlohr Bueso <dave@stgolabs.net>
> > > > Signed-off-by: Andrew Morton <akpm@linux-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.
>
> Nathan,
>
> I am having a hard time reproducing this bug. I had to modify the
> config you pointed me towards with the addition of virtio block device
> support. I tried the next tag you had the issue with along with my most
> recent patches and neither produced the crash. Although I was not able
> to reproduce the crash, I suspect it was to do with insufficient number
> of allocated nodes at fork time. I've been running stress-ng with fork
> & clone in qemu but so far no luck reproducing it.

Sorry about that :( That is odd since my VM appears to be using virtio
block devices?

$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
zram0 252:0 0 7.7G 0 disk [SWAP]
vda 253:0 0 50G 0 disk
├─vda1 253:1 0 600M 0 part /boot/efi
├─vda2 253:2 0 1G 0 part /boot
└─vda3 253:3 0 48.4G 0 part /

> Can you decode the line number of mas_split.isra.0+0x50c/0x784 ?

Sure thing! Here is the entire stacktrace passed through
scripts/decode_stacktrace.sh, this was done at commit fdfbd22f37db ("mm:
start tracking VMAs with maple tree"):

[ 7.473069] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[ 7.473377] Mem abort info:
[ 7.473460] ESR = 0x0000000096000044
[ 7.473595] EC = 0x25: DABT (current EL), IL = 32 bits
[ 7.473765] SET = 0, FnV = 0
[ 7.473867] EA = 0, S1PTW = 0
[ 7.473963] FSC = 0x04: level 0 translation fault
[ 7.474238] Data abort info:
[ 7.474394] ISV = 0, ISS = 0x00000044
[ 7.474574] CM = 0, WnR = 1
[ 7.474737] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000234857000
[ 7.474895] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
[ 7.475717] Internal error: Oops: 96000044 [#1] SMP
[ 7.476094] Modules linked in:
[ 7.476450] CPU: 0 PID: 206 Comm: dracut-rootfs-g Not tainted 5.19.0-rc4+ #1
[ 7.476788] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
[ 7.477085] pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 7.477379] pc : mas_split.isra.0 (lib/maple_tree.c:3303 lib/maple_tree.c:3512)
[ 7.477941] lr : mas_split.isra.0 (lib/maple_tree.c:3543)
[ 7.478136] sp : ffff8000089ab420
[ 7.478269] x29: ffff8000089ab420 x28: ffff0001f4868c80 x27: ffff8000089ab520
[ 7.478620] x26: ffff8000089ab4e0 x25: ffff8000089ab488 x24: ffffd28653819778
[ 7.478884] x23: ffff8000089ab560 x22: ffff8000089ab5a0 x21: ffff8000089ab648
[ 7.479122] x20: 0000000000000002 x19: ffff8000089aba00 x18: 0000000000000002
[ 7.479354] x17: 0000000000000000 x16: ffff0001f485a258 x15: 0000000000000000
[ 7.479662] x14: ffff0001f485aed8 x13: ffff8000089ab658 x12: 0000000000000001
[ 7.479926] x11: ffff8000089ab520 x10: 0000000000000003 x9 : ffff0001f4bb5d00
[ 7.480240] x8 : 000000000000001c x7 : 0000000000000003 x6 : 0000000000000006
[ 7.480638] x5 : ffff0001f4a7e789 x4 : 0000000000000001 x3 : ffff8000089ab4e0
[ 7.480911] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff8000089ab648
[ 7.481254] Call trace:
[ 7.481364] mas_split.isra.0 (lib/maple_tree.c:3303 lib/maple_tree.c:3512)
[ 7.481580] mas_commit_b_node.isra.0 (lib/maple_tree.c:3618)
[ 7.481734] mas_wr_modify (lib/maple_tree.c:4356)
[ 7.481886] mas_wr_store_entry.isra.0 (lib/maple_tree.c:4396)
[ 7.482096] mas_store (lib/maple_tree.c:5651)
[ 7.482265] dup_mmap (kernel/fork.c:707)
[ 7.482410] dup_mm (kernel/fork.c:1539)
[ 7.482554] copy_process (kernel/fork.c:1591 kernel/fork.c:2254)
[ 7.482718] kernel_clone (kernel/fork.c:2669)
[ 7.482878] __do_sys_clone (kernel/fork.c:2804)
[ 7.483072] __arm64_sys_clone (kernel/fork.c:2771)
[ 7.483201] invoke_syscall (./arch/arm64/include/asm/current.h:19 arch/arm64/kernel/syscall.c:57)
[ 7.483361] el0_svc_common.constprop.0 (./arch/arm64/include/asm/daifflags.h:28 arch/arm64/kernel/syscall.c:150)
[ 7.483518] do_el0_svc (arch/arm64/kernel/syscall.c:207)
[ 7.483651] el0_svc (./arch/arm64/include/asm/daifflags.h:28 arch/arm64/kernel/entry-common.c:133 arch/arm64/kernel/entry-common.c:142 arch/arm64/kernel/entry-common.c:625)
[ 7.483767] el0t_64_sync_handler (arch/arm64/kernel/entry-common.c:643)
[ 7.483918] el0t_64_sync (arch/arm64/kernel/entry.S:581)
[ 7.484294] Code: f9000125 f9400e65 9278dca5 f94000a5 (f9000045)
All code
========
0: f9000125 .word 0xf9000125
4: f9400e65 .word 0xf9400e65
8: 9278dca5 .word 0x9278dca5
c: f94000a5 .word 0xf94000a5
10:* f9000045 .word 0xf9000045 <-- trapping instruction

Code starting with the faulting instruction
===========================================
0: f9000045 .word 0xf9000045
[ 7.484865] ---[ end trace 0000000000000000 ]---

> Could you test git tag howlett/maple/20220728 from
> http://git.infradead.org/users/jedix/linux-maple.git and see if this
> issue still triggers?

That tag appears to be okay, so this bug was one you already fixed that
manifested in a different way?

Cheers,
Nathan