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McKenney" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, stable@vger.kernel.org Subject: Re: [PATCH] mm/shmem: report RCU-tasks quiescent states while undoing a range Date: Fri, 18 Sep 2026 17:25:58 -0700 Message-ID: <20260919002559.77365-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260918-shmem-tasks-rcu-v1-1-79acf91a2569@debian.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 068B71C0003 X-Stat-Signature: yyi94siw1qmdb58k9jthnt99mkc4jbju X-HE-Tag: 1789777567-156404 X-HE-Meta: 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 dDneqapM k2gH2LLZiAzgBhaXh7zRwZUmF+u2lpt9XITtQIfTe2eU94CHLdYVJ4VMeMVXT1pnsRxSu861huq15GXNjpszEHJcPlbHPV4avuHM8BcS5VEvhXVYhnFRKgOp12veOUomLeTWSj+XIGnoL9Iz7hhdUhf08h6qjYtcwFIsG89C8ykJ2HtqcQoHscGG9FOal9t2h9Nr1OUlFXHgh29DgO+XEaDxQqQfXc/fat9LrjxYFnIqBWWorcJMuS2OBJOwZs+rucV0U Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 18 Sep 2026 04:24:37 -0700 Breno Leitao wrote: > This shows up in the Meta fleet on ftruncate() of large tmpfs files: > > INFO: rcu_tasks detected stalls on tasks: > 00000000752fd185: .. nvcsw: 59455/59455 holdout: 1 idle_cpu: -1/0 > task:rocksdb:bottom state:R running task > __folio_split > find_get_entry > find_get_entries > truncate_inode_partial_folio > shmem_undo_range > shmem_setattr > notify_change > do_ftruncate > __x64_sys_ftruncate > do_syscall_64 > > shmem_undo_range() walks the whole of the requested range in folio_batch > sized steps, twice, and its two cond_resched() calls are the only > reschedule points in that walk. > > cond_resched() is not an RCU-tasks quiescent state. Use > cond_resched_tasks_rcu_qs() at both points so the walk reports an > RCU-tasks quiescent state as it proceeds. Makes sense to me. Btw I wonder how many cond_resched() will survive from the Mutphy's machine. Just thinking loud. > > Fixes: 8315f42295d2 ("rcu: Add call_rcu_tasks()") > Cc: stable@vger.kernel.org > Signed-off-by: Breno Leitao Reviewed-by: SJ Park Thanks, SJ [...]