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Thu, 02 Feb 2023 02:56:22 -0800 (PST) Received: from C02DW0BEMD6R.bytedance.net ([139.177.225.243]) by smtp.gmail.com with ESMTPSA id 144-20020a621996000000b0058bcb42dd1asm13262409pfz.111.2023.02.02.02.56.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Feb 2023 02:56:21 -0800 (PST) From: Qi Zheng To: akpm@linux-foundation.org, roman.gushchin@linux.dev Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Qi Zheng Subject: [PATCH] mm: shrinkers: fix deadlock in shrinker debugfs Date: Thu, 2 Feb 2023 18:56:12 +0800 Message-Id: <20230202105612.64641-1-zhengqi.arch@bytedance.com> X-Mailer: git-send-email 2.24.3 (Apple Git-128) MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: C191E20024 X-Stat-Signature: cre9domikg4f8i7w89zepqbni554mt8o X-HE-Tag: 1675335383-10991 X-HE-Meta: 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 wmdP0890 Jmg2ITHDvNQBBaH0mq2ljUN+TvQwL5GmMtmVOC1H93wl8EJa89w3EmugU+nCl362wJkfAr6iSeQSlxzIJNO9xmYdkSnLqPdUIKefZohtiGSgLJAUSbiHaL5SbUmrx+hum7SbnEkVP74vLlbDlFqmpe1zVR+bh9+mQ4nlsk/2jUT/O1+1sQtKGXt47z4WfOFEDCErD7L/CxFOqkYEyx8xNEaTW7mZoFQD6LWNXprWpZFDubRGdnFao3MEJbEr6hsymx+cJ4925a271UEQSQbZ8FjfMegIMas7mNKZXVCPwILoGsxtju1orYMZm6zFXbahdE/RkwrreG8q4Jt3X/7pCtXjGjwMWXeZXR7+BjgZPU9jSnHsm2UNB6LX/XQu0aOyozIaTOfbAjA5M6HybHDlJEjH9Q62ulF+r7hzWg7v6fqz8mR3OH4vrM2PGxqWPsCHtiReYJaj6r4kQJDfKMsaiMPnZ1tfN54l0Pw3ZfTnGZOZHmqs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The debugfs_remove_recursive() is invoked by unregister_shrinker(), which is holding the write lock of shrinker_rwsem. It will waits for the handler of debugfs file complete. The handler also needs to hold the read lock of shrinker_rwsem to do something. So it may cause the following deadlock: CPU0 CPU1 debugfs_file_get() shrinker_debugfs_count_show()/shrinker_debugfs_scan_write() unregister_shrinker() --> down_write(&shrinker_rwsem); debugfs_remove_recursive() // wait for (A) --> wait_for_completion(); // wait for (B) --> down_read_killable(&shrinker_rwsem) debugfs_file_put() -- (A) up_write() -- (B) The down_read_killable() can be killed, so that the above deadlock can be recovered. But it still requires an extra kill action, otherwise it will block all subsequent shrinker-related operations, so it's better to fix it. Fixes: 5035ebc644ae ("mm: shrinkers: introduce debugfs interface for memory shrinkers") Signed-off-by: Qi Zheng Reviewed-by: Roman Gushchin --- include/linux/shrinker.h | 4 ++-- mm/shrinker_debug.c | 13 ++++++++----- mm/vmscan.c | 6 +++++- 3 files changed, 15 insertions(+), 8 deletions(-) diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h index 71310efe2fab..0cf3e0d31433 100644 --- a/include/linux/shrinker.h +++ b/include/linux/shrinker.h @@ -107,7 +107,7 @@ extern void synchronize_shrinkers(void); #ifdef CONFIG_SHRINKER_DEBUG extern int shrinker_debugfs_add(struct shrinker *shrinker); -extern void shrinker_debugfs_remove(struct shrinker *shrinker); +extern struct dentry *shrinker_debugfs_remove(struct shrinker *shrinker); extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...); #else /* CONFIG_SHRINKER_DEBUG */ @@ -115,7 +115,7 @@ static inline int shrinker_debugfs_add(struct shrinker *shrinker) { return 0; } -static inline void shrinker_debugfs_remove(struct shrinker *shrinker) +static inline struct dentry *shrinker_debugfs_remove(struct shrinker *shrinker) { } static inline __printf(2, 3) diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c index b05295bab322..39c3491e28a3 100644 --- a/mm/shrinker_debug.c +++ b/mm/shrinker_debug.c @@ -246,18 +246,21 @@ int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...) } EXPORT_SYMBOL(shrinker_debugfs_rename); -void shrinker_debugfs_remove(struct shrinker *shrinker) +struct dentry *shrinker_debugfs_remove(struct shrinker *shrinker) { + struct dentry *entry = shrinker->debugfs_entry; + lockdep_assert_held(&shrinker_rwsem); kfree_const(shrinker->name); shrinker->name = NULL; - if (!shrinker->debugfs_entry) - return; + if (entry) { + ida_free(&shrinker_debugfs_ida, shrinker->debugfs_id); + shrinker->debugfs_entry = NULL; + } - debugfs_remove_recursive(shrinker->debugfs_entry); - ida_free(&shrinker_debugfs_ida, shrinker->debugfs_id); + return entry; } static int __init shrinker_debugfs_init(void) diff --git a/mm/vmscan.c b/mm/vmscan.c index bd6637fcd8f9..74342caf8022 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -741,6 +741,8 @@ EXPORT_SYMBOL(register_shrinker); */ void unregister_shrinker(struct shrinker *shrinker) { + struct dentry *debugfs_entry; + if (!(shrinker->flags & SHRINKER_REGISTERED)) return; @@ -749,9 +751,11 @@ void unregister_shrinker(struct shrinker *shrinker) shrinker->flags &= ~SHRINKER_REGISTERED; if (shrinker->flags & SHRINKER_MEMCG_AWARE) unregister_memcg_shrinker(shrinker); - shrinker_debugfs_remove(shrinker); + debugfs_entry = shrinker_debugfs_remove(shrinker); up_write(&shrinker_rwsem); + debugfs_remove_recursive(debugfs_entry); + kfree(shrinker->nr_deferred); shrinker->nr_deferred = NULL; }