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 4F318433D1; Fri, 30 May 2025 11:39:39 +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=1748605180; cv=none; b=ipRO3XEz2vRK8z1BoeWA6x9U3wEAUnfC3Nhfwg9pD86EawsF0S6sX89xIvKBkk72TVHkQR9BGn8nZ8kNOPWeoF4mj8T/gO7dTST1cdt8uOWEg+PBg2Wwy0p9At0hPDZFRV6UXuEmEY5hRkTloNrOcAew5qJpBfJsXLPxJmIu5wA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748605180; c=relaxed/simple; bh=jiQCGx0YSXrjA7NcSI86rhOwbwWT7bvgPuL9HsaO1e4=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=k4tqbaKbvdRda9ZAk/KydviQKXCX/Jc4OplW53/rjNRRhCDLPdnCwKZbCcaTW8E6CIJqddMN0q74L8y/8VSMjjAHLWqWbX4/549kVEnaGTiHx8wfEw8wbZKId7KhTGcV3bYT0RNYvEymnY8QNp5PfTG9pwJMKuOCDsApJMVn26Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tCzzF4mm; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="tCzzF4mm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAA2AC4CEE9; Fri, 30 May 2025 11:39:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748605179; bh=jiQCGx0YSXrjA7NcSI86rhOwbwWT7bvgPuL9HsaO1e4=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=tCzzF4mm7yxD6Jbk4/3PzRo+HCSmKNujXmH0ycSLDDNnmnayVIWiJv6bMHwDOUQ1c LU5S1Q2J/G47csOds18pPbG1yX/JP2yaK2k3Caqt+FDiCAZdejAq0ALtEiK1zXuBNq /ZsGfnIRf12HfEU52/UEuk1q5nu5VkZLNW9Qp4rgLs+FbbweoWRA4RL3WMsVf3QgTx jAS4erw//R/4aZgnihD+AJveLU1T8MoVXOmnAVmkZvWSiTgCVcwZ6dPlqHcshA/NkJ 7wH3Sd3RQHPtk+iIUe8gpJ+2Qsth6orOljjR0TrRed2jBPO8THEouYd6JDReuHxPid ZCH5g5Rh8/Xqw== Message-ID: <0ae02bf15487f3e5703ce1f5d3107b6dc00477f1.camel@kernel.org> Subject: Re: [PATCH v12 01/10] i915: only initialize struct ref_tracker_dir once From: Jeff Layton To: Krzysztof Karas Cc: Andrew Morton , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Kuniyuki Iwashima , Qasim Ijaz , Nathan Chancellor , Andrew Lunn , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org Date: Fri, 30 May 2025 07:39:36 -0400 In-Reply-To: References: <20250529-reftrack-dbgfs-v12-0-11b93c0c0b6e@kernel.org> <20250529-reftrack-dbgfs-v12-1-11b93c0c0b6e@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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got some warnings from the i915 CI with the ref_tracker debugfs > > patches applied, that indicated that these ref_tracker_dir_init() calls > > were being called more than once. If references were held on these > > objects between the initializations, then that could lead to leaked ref > > tracking objects. > >=20 > > Since these objects are zalloc'ed, ensure that they are only initialize= d > > once by testing whether the first byte of the name field is 0. >=20 > Are you referring to these warnings? > <3> [314.043410] debugfs: File 'intel_wakeref@ffff88815111a308' in direct= ory 'ref_tracker' already present! > <4> [314.043427] ref_tracker: ref_tracker: unable to create debugfs file = for intel_wakeref@ffff88815111a308: -EEXIST >=20 > I think those might be caused by introduction of: > "ref_tracker: automatically register a file in debugfs for a ref_tracker_= dir". >=20 > Current version of "ref_tracker: add a static classname string > to each ref_tracker_dir" further in this series should prevent > multiple calls to "ref_tracker_dir_init()", so this patch could > be dropped I think. > If my reasoning is wrong however, then please add a note to the > commit message which explains why this is needed in more detail > or/and move this patch right before it is necessary. Otherwise > it looks like a vague workaround. >=20 I'm fine with dropping this patch. Those are the messages that demonstrate the problem, but the problem is potentially bigger than those messages. ref_tracker_dir_init() is being called (at least) twice: struct ref_tracker_dir { =20 #ifdef CONFIG_REF_TRACKER =20 spinlock_t lock; =20 unsigned int quarantine_avail; =20 refcount_t untracked; =20 refcount_t no_tracker; =20 bool dead; =20 struct list_head list; /* List of active trackers */ =20 struct list_head quarantine; /* List of dead trackers */ const char *class; /* object classname */ =20 #ifdef CONFIG_DEBUG_FS =20 struct dentry *dentry; =20 struct dentry *symlink; =20 #endif =20 #endif =20 };=C2=A0 This structure contains two list_heads that can contain ref_tracker objects. If that list was populated when ref_tracker_dir_init() is called the second time, then those objects will now be sitting on a corrupt list. At best they'll just leak, but with them sitting on a now-corrupt list, they could cause a panic too. It may be that there can be no objects on that list when it's called the second time. But with this patchset initializing it twice will cause dentry leaks at least. --=20 Jeff Layton