linux-kernel - [BUG] trigger BUG_ON in mas_store

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Message-ID: <9cb8c599b1d7f9c1c300d1a334d5eb70ec4d7357.camel@mediatek.com>
Date:   Fri, 9 Jun 2023 08:37:31 +0000
From:   John Hsu (許永翰) <John.Hsu@...iatek.com>
To:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "liam.howlett@...cle.com" <liam.howlett@...cle.com>
CC:     Andrew Yang (楊智強) 
        <Andrew.Yang@...iatek.com>,
        Qun-wei Lin (林群崴) 
        <Qun-wei.Lin@...iatek.com>,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        Casper Li (李中榮) <casper.li@...iatek.com>,
        Kuan-Ying Lee (李冠穎) 
        <Kuan-Ying.Lee@...iatek.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "yuzhao@...gle.com" <yuzhao@...gle.com>,
        John Hsu (許永翰) <John.Hsu@...iatek.com>
Subject: [BUG] trigger BUG_ON in mas_store_prealloc when low memory

Hi reviewers and author liam.howlett@...cle.com,
Kindly ping.

We met BUG_ON in mas_store_prealloc with kernel-6.1 stress testing
environment.
According to coredump, BUG_ON is triggered by mas->node with error
number -ENOMEM(0xffffffffffffffd2).
There are some mas_node_count functions in mas_wr_store_entry, and it
seems that mas->node may be set to error node with -ENOMEM if there was
no enough memory spcace for maple tree operations.
We think that return -ENOMEM instead of directly triggering BUG_ON when
memory is not available is suitable, because in reality the tree
operation shouldn't be performed in this situation.

following are the backtrace:
mas_store_prealloc+0x23c/0x484
vma_mas_store+0xe4/0x2d0
__vma_adjust+0xab0/0x1470
vma_merge+0x5b8/0x5d4
mprotect_fixup+0x1f4/0x478
__arm64_sys_mprotect+0x6b0/0x8f0
invoke_syscall+0x84/0x264
el0_svc_common+0x118/0x1f0
do_el0_svc+0x5c/0x184
el0_svc+0x38/0x98

Any suggestion is appreciated.

Thank you.
BRs,
John Hsu