linux-kernel - Re: [PATCH v7 00/70] Introducing the Maple Tree

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Message-ID: <20220419231748.omnhkl43vl5ep2j5@revolver>
Date:   Tue, 19 Apr 2022 23:18:02 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Yu Zhao <yuzhao@...gle.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        "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>
Subject: Re: [PATCH v7 00/70] Introducing the Maple Tree

* Yu Zhao <yuzhao@...gle.com> [220419 17:59]:
> On Tue, Apr 19, 2022 at 9:51 AM Liam Howlett <liam.howlett@...cle.com> wrote:
> >
> > * Yu Zhao <yuzhao@...gle.com> [220416 15:30]:
> > > On Sat, Apr 16, 2022 at 9:19 AM Liam Howlett <liam.howlett@...cle.com> wrote:
> > > >
> > >
> > > <snipped>
> > >
> > > > How did you hit this issue?  Just on boot?
> > >
> > > I was hoping this is known to you or you have something I can verify for you.
> >
> >
> > Thanks, yes.  I believe that both crashes are the same root cause.  The
> > cause is that I was not cleaning up after the kmem bulk allocation
> > failure on my side.  Please test with this patch.
> 
> Thanks. I applied this patch and hit a LOCKDEP and then a BUG_ON:
> 
>   lib/maple_tree.c:847 suspicious rcu_dereference_protected() usage!
>   Call Trace:
>    <TASK>
>    dump_stack_lvl+0x6c/0x9a
>    dump_stack+0x10/0x12
>    lockdep_rcu_suspicious+0x12c/0x140
>    __mt_destroy+0x96/0xd0
>    exit_mmap+0x2a0/0x360
>    __mmput+0x34/0x100
>    mmput+0x2f/0x40
>    free_bprm+0x64/0xe0
>    kernel_execve+0x129/0x330
>    call_usermodehelper_exec_async+0xd8/0x130
>    ? proc_cap_handler+0x210/0x210
>    ret_from_fork+0x1f/0x30
>    </TASK>

Thanks - I'm not sure how this got through, but this should fix it.

This should be added to 4236a642ad185 to avoid the LOCKDEP issue.

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3163,9 +3163,9 @@ void exit_mmap(struct mm_struct *mm)
 
        BUG_ON(count != mm->map_count);
 
-       mmap_write_unlock(mm);
        trace_exit_mmap(mm);
        __mt_destroy(&mm->mm_mt);
+       mmap_write_unlock(mm);
        vm_unacct_memory(nr_accounted);
 }

> 
>   BUG: unable to handle page fault for address: ffffa6072aff0060
>   RIP: 0010:mab_calc_split+0x103/0x1a0
>   Code: 29 c1 8b 86 64 02 00 00 0f b6 80 dc 7d a7 96 39 c1 7e 05 83 c3
> 01 eb 06 81 c3 ff 00 00 00 0f b6 c3 45 84 d2 74 3f 41 0f b6 ca <48> 83
> bc ce 10 01 00 00 00 75 2d 41 83 c0 ff 41 39 c8 7e 20 0f b6
>   RSP: 0018:ffffa6072afef6d0 EFLAGS: 00010286
>   RAX: 0000000000000054 RBX: 0000000000000154 RCX: 00000000000000aa
>   RDX: ffffa6072afef83f RSI: ffffa6072afefa00 RDI: ffffa6072afefe80
>   RBP: ffffa6072afef6e0 R08: 0000000000000010 R09: 00000000000000ff
>   R10: 00000000000000aa R11: 0000000000000001 R12: 00000000000000ff
>   R13: ffffa6072afefa00 R14: ffffa6072afef9c0 R15: 0000000000000008
>   FS:  0000000001d75340(0000) GS:ffff8a56bf980000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: ffffa6072aff0060 CR3: 00000004986ca002 CR4: 00000000001706e0
>   Call Trace:
>    <TASK>
>    mas_spanning_rebalance+0x416/0x2060
>    mas_wr_store_entry+0xa6d/0xa80
>    mas_store_gfp+0xf6/0x170
>    do_mas_align_munmap+0x32b/0x5c0
>    do_mas_munmap+0xf3/0x110
>    __vm_munmap+0xd4/0x180
>    __x64_sys_munmap+0x1b/0x20
>    do_syscall_64+0x44/0xa0
> 
> $ ./scripts/faddr2line vmlinux mab_calc_split+0x103
> mab_calc_split+0x103/0x1a0:
> mab_no_null_split at lib/maple_tree.c:1787
> (inlined by) mab_calc_split at lib/maple_tree.c:1866

1787 is "if (!b_node->slot[split]) {"  Does this line up with your code?
How did you trigger this?