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[83.42.47.173]) by smtp.gmail.com with ESMTPSA id n7-20020adffe07000000b003176c6e87b1sm3406455wrr.81.2023.07.25.17.08.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Jul 2023 17:08:28 -0700 (PDT) From: =?UTF-8?q?Joan=20Bruguera=20Mic=C3=B3?= To: Steven Price Cc: zhengqi.arch@bytedance.com, "Matthew Wilcox (Oracle)" , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH] mm: shrinkers: fix race condition on debugfs cleanup Date: Wed, 26 Jul 2023 00:08:26 +0000 Message-ID: <20230726000827.724389-1-joanbrugueram@gmail.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: q98qu6hpqj468txs8zpixrrbqgga9ho9 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: CC63920002 X-HE-Tag: 1690330110-204624 X-HE-Meta: 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 SU7Wk6Ni 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.022861, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hmmm, indeed linux-next crashes with a null pointer dereference when calling `ida_free(..., -1)`. It appears to me that 69cb69ea5542 ("ida: Remove assertions that an ID was allocated") didn't intend to make `ida_free(..., -1)` invalid; after all, it was authored & introduced immediately after fc82bbf4dede ("ida: don't use BUG_ON() for debugging") whose commit message calls for making it legal, with Matthew's support. And the referenced Bluetooth HCI code that also calls `ida_free(..., -1)` is still there, as far as I can tell ([1]). Rather, probably the `((int)id < 0)` was accidentally dropped, or the idea was that it would be handled by the `not_found:` label in `ida_free`, but for that to work you'd need to change the `!test_bit(bit, bitmap->bitmap)` condition to `!bitmap || !test_bit(bit, bitmap->bitmap)` since otherwise `bitmap->bitmap` is a null pointer dereference. I will send a patch to get it fixed. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/bluetooth/hci_sock.c#n106