linux-kernel - Re: [PATCH 2/7] genalloc: selftest

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Message-ID: <aa491cf5-ace4-1e2c-2f49-60f96b1e6da9@huawei.com>
Date:   Mon, 26 Feb 2018 21:26:58 +0200
From:   Igor Stoppa <igor.stoppa@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     J Freyensee <why2jjj.linux@...il.com>, <david@...morbit.com>,
        <keescook@...omium.org>, <mhocko@...nel.org>, <labbott@...hat.com>,
        <linux-security-module@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 2/7] genalloc: selftest

On 26/02/18 21:12, Matthew Wilcox wrote:
[...]

> panic() halts the kernel
> BUG_ON() kills the thread
> WARN_ON() just prints messages
> 
> Now, if we're at boot time and we're still executing code from the init
> thread, killing init is equivalent to halting the kernel.
> 
> The question is, what is appropriate for test modules?  I would say
> WARN_ON is not appropriate because people ignore warnings.  BUG_ON is
> reasonable for development.  panic() is probably not.

Ok, so I can leave WARN_ON() in the libraries, and keep the more
restrictive BUG_ON() for the self test, which is optional for both
genalloc and pmalloc.

> Also, calling BUG_ON while holding a lock is not a good idea; if anything
> needs to acquire that lock to shut down in a reasonable fashion, it's
> going to hang.
> 
> And there's no need to do something like BUG_ON(!foo); foo->wibble = 1;
> Dereferencing a NULL pointer already produces a nice informative splat.
> In general, we assume other parts of the kernel are sane and if they pass
> us a NULL pool, it's no good returning -EINVAL, we may as well just oops
> and let somebody else debug it.

Great, that makes the code even simpler.

--
igor