From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DE02A2EF281; Tue, 17 Jun 2025 16:21:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750177306; cv=none; b=Bpfsw4ImFeB5la3toFsP7VIwzStRUM7H6iw+yDkAcsQcPATscI2neZgYxZUbJvc2bmFHxeuYExWkXHY4IhOmLqkWIf0ZWFe3ETw4qhpOdnTeZi4kfhEwwb+pTmf4cBASaRxAeHW+VHnJ5yVQ+8nrpvQHjQvmrdUl75wp/BZdeqY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750177306; c=relaxed/simple; bh=6IF5JfJhBrr5zgJSYos60XQLyphNjvQ5eMSy+hr7Nss=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=YAMPYobiXoxfvMpiO2aI6akaCOkXE7Lzlq5iF8GXem1v0r1YTNVMdQxvjbnoMAR4DPpDdZYZ1bxYUEit9jXpBk6wNcXpi+lV6XELJaZBruCKeFNCdOQZ+mTFW0x4P94dgQ5VmFDZ5FnLMmvQuEhA1H5kGMWsHyM9c7pndgxwG00= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=w1uhU4ur; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="w1uhU4ur" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 584DEC4CEE3; Tue, 17 Jun 2025 16:21:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1750177305; bh=6IF5JfJhBrr5zgJSYos60XQLyphNjvQ5eMSy+hr7Nss=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=w1uhU4urUxX0UlAkKV5qcgXSlVpJrpgFNRHJZp3V2aPGuW5BsjdCQI7yfrcietVS1 4ieYDJMCBDMza8YJIrCBEt2Ix445gTGy1/Jj68PtfbqWFz3fsWRLPTFME53UFjgwQ4 i5E8DorSk03MeFw54qmU+kMx/8XnUdvwtpAWRR1I= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chen Ridong , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Tejun Heo , Sasha Levin Subject: [PATCH 6.15 287/780] kernfs: Relax constraint in draining guard Date: Tue, 17 Jun 2025 17:19:55 +0200 Message-ID: <20250617152503.157635900@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250617152451.485330293@linuxfoundation.org> References: <20250617152451.485330293@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michal Koutný [ Upstream commit 071d8e4c2a3b0999a9b822e2eb8854784a350f8a ] The active reference lifecycle provides the break/unbreak mechanism but the active reference is not truly active after unbreak -- callers don't use it afterwards but it's important for proper pairing of kn->active counting. Assuming this mechanism is in place, the WARN check in kernfs_should_drain_open_files() is too sensitive -- it may transiently catch those (rightful) callers between kernfs_unbreak_active_protection() and kernfs_put_active() as found out by Chen Ridong: kernfs_remove_by_name_ns kernfs_get_active // active=1 __kernfs_remove // active=0x80000002 kernfs_drain ... wait_event //waiting (active == 0x80000001) kernfs_break_active_protection // active = 0x80000001 // continue kernfs_unbreak_active_protection // active = 0x80000002 ... kernfs_should_drain_open_files // warning occurs kernfs_put_active To avoid the false positives (mind panic_on_warn) remove the check altogether. (This is meant as quick fix, I think active reference break/unbreak may be simplified with larger rework.) Fixes: bdb2fd7fc56e1 ("kernfs: Skip kernfs_drain_open_files() more aggressively") Link: https://lore.kernel.org/r/kmmrseckjctb4gxcx2rdminrjnq2b4ipf7562nvfd432ld5v5m@2byj5eedkb2o/ Cc: Chen Ridong Signed-off-by: Michal Koutný Acked-by: Tejun Heo Link: https://lore.kernel.org/r/20250505121201.879823-1-mkoutny@suse.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- fs/kernfs/dir.c | 5 +++-- fs/kernfs/file.c | 3 ++- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index fc70d72c3fe80..43487fa83eaea 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1580,8 +1580,9 @@ void kernfs_break_active_protection(struct kernfs_node *kn) * invoked before finishing the kernfs operation. Note that while this * function restores the active reference, it doesn't and can't actually * restore the active protection - @kn may already or be in the process of - * being removed. Once kernfs_break_active_protection() is invoked, that - * protection is irreversibly gone for the kernfs operation instance. + * being drained and removed. Once kernfs_break_active_protection() is + * invoked, that protection is irreversibly gone for the kernfs operation + * instance. * * While this function may be called at any point after * kernfs_break_active_protection() is invoked, its most useful location diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 66fe8fe41f060..a6c692cac6165 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -778,8 +778,9 @@ bool kernfs_should_drain_open_files(struct kernfs_node *kn) /* * @kn being deactivated guarantees that @kn->attr.open can't change * beneath us making the lockless test below safe. + * Callers post kernfs_unbreak_active_protection may be counted in + * kn->active by now, do not WARN_ON because of them. */ - WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS); rcu_read_lock(); on = rcu_dereference(kn->attr.open); -- 2.39.5