The patch titled Subject: mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS has been added to the -mm tree. Its filename is mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Michal Hocko <mhocko@xxxxxxxx> Subject: mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS Tetsuo Handa has noticed that MMF_UNSTABLE SIGBUS path in handle_mm_fault causes a lockdep splat [ 58.539455] Out of memory: Kill process 1056 (a.out) score 603 or sacrifice child [ 58.543943] Killed process 1056 (a.out) total-vm:4268108kB, anon-rss:2246048kB, file-rss:0kB, shmem-rss:0kB [ 58.544245] a.out (1169) used greatest stack depth: 11664 bytes left [ 58.557471] DEBUG_LOCKS_WARN_ON(depth <= 0) [ 58.557480] ------------[ cut here ]------------ [ 58.564407] WARNING: CPU: 6 PID: 1339 at kernel/locking/lockdep.c:3617 lock_release+0x172/0x1e0 [ 58.599401] CPU: 6 PID: 1339 Comm: a.out Not tainted 4.13.0-rc3-next-20170803+ #142 [ 58.604126] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015 [ 58.609790] task: ffff9d90df888040 task.stack: ffffa07084854000 [ 58.613944] RIP: 0010:lock_release+0x172/0x1e0 [ 58.617622] RSP: 0000:ffffa07084857e58 EFLAGS: 00010082 [ 58.621533] RAX: 000000000000001f RBX: ffff9d90df888040 RCX: 0000000000000000 [ 58.626074] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffa30d4ba4 [ 58.630572] RBP: ffffa07084857e98 R08: 0000000000000000 R09: 0000000000000001 [ 58.635016] R10: 0000000000000000 R11: 000000000000001f R12: ffffa07084857f58 [ 58.639694] R13: ffff9d90f60d6cd0 R14: 0000000000000000 R15: ffffffffa305cb6e [ 58.644200] FS: 00007fb932730740(0000) GS:ffff9d90f9f80000(0000) knlGS:0000000000000000 [ 58.648989] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 58.652903] CR2: 000000000040092f CR3: 0000000135229000 CR4: 00000000000606e0 [ 58.657280] Call Trace: [ 58.659989] up_read+0x1a/0x40 [ 58.662825] __do_page_fault+0x28e/0x4c0 [ 58.665946] do_page_fault+0x30/0x80 [ 58.668911] page_fault+0x28/0x30 The reason is that the page fault path might have dropped the mmap_sem and returned with VM_FAULT_RETRY. MMF_UNSTABLE check however rewrites the error path to VM_FAULT_SIGBUS and we always expect mmap_sem taken in that path. Fix this by taking mmap_sem when VM_FAULT_RETRY is held in the MMF_UNSTABLE path. We cannot simply add VM_FAULT_SIGBUS to the existing error code because all arch specific page fault handlers and g-u-p would have to learn a new error code combination. Link: http://lkml.kernel.org/r/20170807113839.16695-2-mhocko@xxxxxxxxxx Fixes: 3f70dc38cec2 ("mm: make sure that kthreads will not refault oom reaped memory") Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Cc: Andrea Argangeli <andrea@xxxxxxxxxx> Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Wenwei Tao <wenwei.tww@xxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [4.9+] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memory.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff -puN mm/memory.c~mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus mm/memory.c --- a/mm/memory.c~mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus +++ a/mm/memory.c @@ -3910,8 +3910,18 @@ int handle_mm_fault(struct vm_area_struc * further. */ if (unlikely((current->flags & PF_KTHREAD) && !(ret & VM_FAULT_ERROR) - && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags))) + && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags))) { + + /* + * We are going to enforce SIGBUS but the PF path might have + * dropped the mmap_sem already so take it again so that + * we do not break expectations of all arch specific PF paths + * and g-u-p + */ + if (ret & VM_FAULT_RETRY) + down_read(&vma->vm_mm->mmap_sem); ret = VM_FAULT_SIGBUS; + } return ret; } _ Patches currently in -mm which might be from mhocko@xxxxxxxx are mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus.patch mm-oom-fix-potential-data-corruption-when-oom_reaper-races-with-writer.patch mm-memory_hotplug-display-allowed-zones-in-the-preferred-ordering.patch mm-memory_hotplug-remove-zone-restrictions.patch mm-page_alloc-rip-out-zonelist_order_zone.patch mm-page_alloc-remove-boot-pageset-initialization-from-memory-hotplug.patch mm-page_alloc-do-not-set_cpu_numa_mem-on-empty-nodes-initialization.patch mm-memory_hotplug-drop-zone-from-build_all_zonelists.patch mm-memory_hotplug-remove-explicit-build_all_zonelists-from-try_online_node.patch mm-page_alloc-simplify-zonelist-initialization.patch mm-page_alloc-remove-stop_machine-from-build_all_zonelists.patch mm-memory_hotplug-get-rid-of-zonelists_mutex.patch mm-sparse-page_ext-drop-ugly-n_high_memory-branches-for-allocations.patch mm-vmscan-do-not-loop-on-too_many_isolated-for-ever.patch mm-vmscan-do-not-loop-on-too_many_isolated-for-ever-fix.patch treewide-remove-gfp_temporary-allocation-flag.patch mm-rename-global_page_state-to-global_zone_page_state.patch mm-hugetlb-do-not-allocate-non-migrateable-gigantic-pages-from-movable-zones.patch mm-oom-do-not-rely-on-tif_memdie-for-memory-reserves-access.patch mm-replace-tif_memdie-checks-by-tsk_is_oom_victim.patch fs-proc-remove-priv-argument-from-is_stack.patch