On 1/2/19 12:30 PM, Jan Stancek wrote:
> Hi,
>
> LTP move_pages12 [1] started failing recently.
>
> The test maps/unmaps some anonymous private huge pages
> and migrates them between 2 nodes. This now reliably
> hits NULL ptr deref:
>
> [ 194.819357] BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
> [ 194.864410] #PF error: [WRITE]
> [ 194.881502] PGD 22c758067 P4D 22c758067 PUD 235177067 PMD 0
> [ 194.913833] Oops: 0002 [#1] SMP NOPTI
> [ 194.935062] CPU: 0 PID: 865 Comm: move_pages12 Not tainted 4.20.0+ #1
> [ 194.972993] Hardware name: HP ProLiant SL335s G7/, BIOS A24 12/08/2012
> [ 195.005359] RIP: 0010:down_write+0x1b/0x40
> [ 195.028257] Code: 00 5c 01 00 48 83 c8 03 48 89 43 20 5b c3 90 0f 1f 44 00 00 53 48 89 fb e8 d2 d7 ff ff 48 89 d8 48 ba 01 00 00 00 ff ff
> ff ff <f0> 48 0f c1 10 85 d2 74 05 e8 07 26 ff ff 65 48 8b 04 25 00 5c 01
> [ 195.121836] RSP: 0018:ffffb87e4224fd00 EFLAGS: 00010246
> [ 195.147097] RAX: 0000000000000030 RBX: 0000000000000030 RCX: 0000000000000000
> [ 195.185096] RDX: ffffffff00000001 RSI: ffffffffa69d30f0 RDI: 0000000000000030
> [ 195.219251] RBP: 0000000000000030 R08: ffffe7d4889d8008 R09: 0000000000000003
> [ 195.258291] R10: 000000000000000f R11: ffffe7d4889d8008 R12: ffffe7d4889d0008
> [ 195.294547] R13: ffffe7d490b78000 R14: ffffe7d4889d0000 R15: ffff8be9b2ba4580
> [ 195.332532] FS: 00007f1670112b80(0000) GS:ffff8be9b7a00000(0000) knlGS:0000000000000000
> [ 195.373888] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 195.405938] CR2: 0000000000000030 CR3: 000000023477e000 CR4: 00000000000006f0
> [ 195.443579] Call Trace:
> [ 195.456876] migrate_pages+0x833/0xcb0
> [ 195.478070] ? __ia32_compat_sys_migrate_pages+0x20/0x20
> [ 195.506027] do_move_pages_to_node.isra.63.part.64+0x2a/0x50
> [ 195.536963] kernel_move_pages+0x667/0x8c0
> [ 195.559616] ? __handle_mm_fault+0xb95/0x1370
> [ 195.588765] __x64_sys_move_pages+0x24/0x30
> [ 195.611439] do_syscall_64+0x5b/0x160
> [ 195.631901] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 195.657790] RIP: 0033:0x7f166f5ff959
> [ 195.676365] Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08
> 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 17 45 2c 00 f7 d8 64 89 01 48
> [ 195.772938] RSP: 002b:00007ffd8d77bb48 EFLAGS: 00000246 ORIG_RAX: 0000000000000117
> [ 195.810207] RAX: ffffffffffffffda RBX: 0000000000000400 RCX: 00007f166f5ff959
> [ 195.847522] RDX: 0000000002303400 RSI: 0000000000000400 RDI: 0000000000000360
> [ 195.882327] RBP: 0000000000000400 R08: 0000000002306420 R09: 0000000000000004
> [ 195.920017] R10: 0000000002305410 R11: 0000000000000246 R12: 0000000002303400
> [ 195.958053] R13: 0000000002305410 R14: 0000000002306420 R15: 0000000000000003
> [ 195.997028] Modules linked in: sunrpc amd64_edac_mod ipmi_ssif edac_mce_amd kvm_amd ipmi_si igb ipmi_devintf k10temp kvm pcspkr ipmi_msgha
> ndler joydev irqbypass sp5100_tco dca hpwdt hpilo i2c_piix4 xfs libcrc32c radeon i2c_algo_bit drm_kms_helper ttm ata_generic pata_acpi drm se
> rio_raw pata_atiixp
> [ 196.134162] CR2: 0000000000000030
> [ 196.152788] ---[ end trace 4420ea5061342d3e ]---
>
> Suspected commit is:
> b43a99900559 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization")
> which adds to unmap_and_move_huge_page():
> + struct address_space *mapping = page_mapping(hpage);
> +
> + /*
> + * try_to_unmap could potentially call huge_pmd_unshare.
> + * Because of this, take semaphore in write mode here and
> + * set TTU_RMAP_LOCKED to let lower levels know we have
> + * taken the lock.
> + */
> + i_mmap_lock_write(mapping);
>
> If I'm reading this right, 'mapping' will be NULL for anon mappings.
Not exactly.
In the anon case mapping will point to a 'struct anon_vma *'. But,
i_mmap_lock_write expects a 'struct address_space *'. I believe this
is source of the NULL pointer dereference in down_write.
Not sure what is happening in the MAP_SHARED case. My test which does
something similar does not have issues.
In any case, the commit is bad. I will investagate further.
--
Mike Kravetz
> Running same test with s/MAP_PRIVATE/MAP_SHARED/ leads to user-space
> hanging at:
>
> # cat /proc/23654/stack
> [<0>] io_schedule+0x12/0x40
> [<0>] __lock_page+0x13c/0x200
> [<0>] remove_inode_hugepages+0x275/0x300
> [<0>] hugetlbfs_evict_inode+0x2e/0x60
> [<0>] evict+0xcb/0x190
> [<0>] __dentry_kill+0xce/0x160
> [<0>] dentry_kill+0x47/0x170
> [<0>] dput.part.33+0xc6/0x100
> [<0>] __fput+0x105/0x230
> [<0>] task_work_run+0x84/0xa0
> [<0>] exit_to_usermode_loop+0xd3/0xe0
> [<0>] do_syscall_64+0x14d/0x160
> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [<0>] 0xffffffffffffffff
>
> # cat /proc/23655/stack
> [<0>] call_rwsem_down_read_failed+0x14/0x30
> [<0>] rmap_walk_file+0x1c1/0x2f0
> [<0>] remove_migration_ptes+0x6d/0x80
> [<0>] migrate_pages+0x86a/0xcb0
> [<0>] do_move_pages_to_node.isra.63.part.64+0x2a/0x50
> [<0>] kernel_move_pages+0x667/0x8c0
> [<0>] __x64_sys_move_pages+0x24/0x30
> [<0>] do_syscall_64+0x5b/0x160
> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [<0>] 0xffffffffffffffff
>
> Regards,
> Jan
>
> [1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/move_pages/move_pages12.c
>
