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From: Matthew Wilcox <willy@infradead.org>
To: Jeff Layton <jlayton@kernel.org>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
	lhenriques@suse.com, cmaiolino@redhat.com,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] mm: check for sleepable context in kvfree
Date: Tue, 23 Jul 2019 11:11:24 -0700	[thread overview]
Message-ID: <20190723181124.GM363@bombadil.infradead.org> (raw)
In-Reply-To: <f43c131d9b635994aafed15cb72308b32d2eef67.camel@kernel.org>

On Tue, Jul 23, 2019 at 02:05:11PM -0400, Jeff Layton wrote:
> On Tue, 2019-07-23 at 10:55 -0700, Matthew Wilcox wrote:
> > > HCH points out that xfs uses kvfree as a generic "free this no matter
> > > what it is" sort of wrapper and expects the callers to work out whether
> > > they might be freeing a vmalloc'ed address. If that sort of usage turns
> > > out to be prevalent, then we may need another approach to clean this up.
> > 
> > I think it's a bit of a landmine, to be honest.  How about we have kvfree()
> > call vfree_atomic() instead?
> 
> Not a bad idea, though it means more overhead for the vfree case.
> 
> Since we're spitballing here...could we have kvfree figure out whether
> it's running in a context where it would need to queue it instead and
> only do it in that case?
> 
> We currently have to figure that out for the might_sleep_if anyway. We
> could just have it DTRT instead of printk'ing and dumping the stack in
> that case.

I don't think we have a generic way to determine if we're currently
holding a spinlock.  ie this can fail:

spin_lock(&my_lock);
kvfree(p);
spin_unlock(&my_lock);

If we're preemptible, we can check the preempt count, but !CONFIG_PREEMPT
doesn't record the number of spinlocks currently taken.

  reply	other threads:[~2019-07-23 18:11 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-23 13:12 [PATCH] mm: check for sleepable context in kvfree Jeff Layton
2019-07-23 17:52 ` Jeff Layton
2019-07-23 17:55   ` Matthew Wilcox
2019-07-23 18:05     ` Jeff Layton
2019-07-23 18:11       ` Matthew Wilcox [this message]
2019-07-23 18:19         ` Jeff Layton
2019-07-23 18:29           ` Matthew Wilcox

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