From: Borislav Petkov <bp@alien8.de>
To: Xiaochen Shen <xiaochen.shen@intel.com>
Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
tony.luck@intel.com, fenghua.yu@intel.com,
reinette.chatre@intel.com, x86@kernel.org,
linux-kernel@vger.kernel.org, pei.p.jia@intel.com
Subject: Re: [PATCH] x86/resctrl: Fix potential lockdep warning
Date: Wed, 13 Nov 2019 12:44:14 +0100 [thread overview]
Message-ID: <20191113114334.GA1647@zn.tnic> (raw)
In-Reply-To: <1573079796-11713-1-git-send-email-xiaochen.shen@intel.com>
On Thu, Nov 07, 2019 at 06:36:36AM +0800, Xiaochen Shen wrote:
> rdtgroup_cpus_write() and mkdir_rdt_prepare() call
> rdtgroup_kn_lock_live() -> kernfs_to_rdtgroup() to get 'rdtgrp', and
> then call rdt_last_cmd_xxx() functions which will check if
Write those names like this:
rdt_last_cmd_{clear,puts,...} but not with an "xxx" which confuses
people unfamiliar with the code.
> rdtgroup_mutex is held/requires its caller to hold rdtgroup_mutex.
> But if 'rdtgrp' returned from kernfs_to_rdtgroup() is NULL,
> rdtgroup_mutex is not held and calling rdt_last_cmd_xxx() will result
> in a lockdep warning.
That's more of a self-incurred lockdep warning. You can't be calling
lockdep_assert_held() after a function which doesn't always grab the
mutex. Looks like the design needs changing here...
> Remove rdt_last_cmd_xxx() in these two paths. Just returning error
> should be sufficient to report to the user that the entry doesn't exist
> any more.
... or that.
In any case, you should consider fixing such patterns in the code as it
looks sub-optimal from where I'm standing.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2019-11-13 11:44 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 22:36 [PATCH] x86/resctrl: Fix potential lockdep warning Xiaochen Shen
2019-11-13 11:44 ` Borislav Petkov [this message]
2019-11-16 16:13 ` Xiaochen Shen
2019-11-18 15:02 ` Borislav Petkov
2019-11-19 7:44 ` Xiaochen Shen
2019-11-13 11:47 ` [tip: x86/urgent] " tip-bot2 for Xiaochen Shen
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