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b=cBxhYKn24E4Wff8v3kXMyY9v06fkDcfNPYR13C38R/VJGwODif4B3dVKpG80pUgxo GXfocFV0PN11rCXvgqvSsSJYTfaUPVJDqCSecYbITJRuoDlepAjKMo1zuywuCdIObE IftviacLyiYyKDbEl8ibEIa0chNKayx/bs8Ge6qs= Date: Mon, 27 Apr 2026 03:43:52 -0700 From: Andrew Morton To: Qi Zheng Cc: shakeel.butt@linux.dev, syzbot , Liam.Howlett@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, surenb@google.com, syzkaller-bugs@googlegroups.com, vbabka@kernel.org, Muchun Song Subject: Re: [syzbot] [mm?] WARNING: bad unlock balance in do_wp_page Message-Id: <20260427034352.6ca48156d613319aac415290@linux-foundation.org> In-Reply-To: <3591c663-a4a9-4c22-97cf-b58b2e7d8a41@linux.dev> References: <69edca15.170a0220.38e3f1.0000.GAE@google.com> <20260426034938.db29d74982a8eb8463f8cf3a@linux-foundation.org> <20260426105532.43768b24a42744f1b52fdff2@linux-foundation.org> <3591c663-a4a9-4c22-97cf-b58b2e7d8a41@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: EBBE81C0004 X-Rspamd-Server: rspam04 X-Stat-Signature: jqadaxsm8mq58hdcpbbmde66dwmgeinb X-HE-Tag: 1777286634-460959 X-HE-Meta: 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 PSDSTnCG azDTqdD0Lpq+1awiaCCp/WnXnIbUr3mdoTRchwEotYubTJZHkRR3lwa04nDJaJeHKDXP8UukspfWqmuI2yO5cc/yQBJABzXEDmjjmnqHsi7C/zLprhi7UzhVSqJJyrfD3/totpIsFTXMDrdUn93F4E7lV2uhr7TMvIV17RD6XFdF9uUENh+7YpOS5mA1V7hOBdZSaQe1tPXS5HGgGoE1cUqzfG75AGF5DJe34qSsrkpg/TxGOnKFLsWtUlefCqdjpXsCH8mgQ3WAK88dgqQ5/ToX7JGJYz/9PwVgB9+D/vmtPeHnIfLb7BKrnSUwSWiFf/dWIRNiBIvyd47htnJyrGhdZKwutiatEU/Ri46nsOXma+dNPYjyR9z32o/TIe0P6+ewGI6MgulQhr9oQbR4rFI0W/fP0AOp7S1fm/IeI3UMU6iG5bcaahhp3miLNg8ubTLDd7W69KeCW1nTQ1s/3vtrxLlAlhbSG5ngX Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 27 Apr 2026 15:24:10 +0800 Qi Zheng wrote: > > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -805,10 +805,15 @@ static long memcg_state_val_in_pages(int idx, long > val) > * Used in mod_memcg_state() and mod_memcg_lruvec_state() to avoid > race with > * reparenting of non-hierarchical state_locals. > */ > -static inline struct mem_cgroup *get_non_dying_memcg_start(struct > mem_cgroup *memcg) > +static inline struct mem_cgroup *get_non_dying_memcg_start(struct > mem_cgroup *memcg, > + bool *locked) Sometimes this is called "locked", sometimes "rcu_locked". Let's be consistent please. > { > - if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) > + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) { > + *locked = false; > return memcg; > + } I was thinking we could use a single bit in the task_struct for this: --- a/mm/memcontrol.c~a +++ a/mm/memcontrol.c @@ -810,6 +810,8 @@ static inline struct mem_cgroup *get_non if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) return memcg; + current->foo = 1; + rcu_read_lock(); while (memcg_is_dying(memcg)) @@ -820,9 +822,11 @@ static inline struct mem_cgroup *get_non static inline void get_non_dying_memcg_end(void) { - if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) + if (current->foo == 0) return; + current->foo = 0; + rcu_read_unlock(); } #else _ That doesn't work if get_non_dying_memcg_start/get_non_dying_memcg_end calls can nest? If they can nest then we'd need a counter in the task_struct.