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SubjectRe: [PATCH] mm: Make kvfree safe to call
On Fri, Jul 26, 2019 at 2:01 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> Since vfree() can sleep, calling kvfree() from contexts where sleeping
> is not permitted (eg holding a spinlock) is a bit of a lottery whether
> it'll work. Introduce kvfree_safe() for situations where we know we can
> sleep, but make kvfree() safe by default.
>
> Reported-by: Jeff Layton <jlayton@kernel.org>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Luis Henriques <lhenriques@suse.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Carlos Maiolino <cmaiolino@redhat.com>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

So you say you are adding kvfree_safe() in the patch description, but
it looks like you are introducing kvfree_fast() below. Did something
change and the patch description wasn't updated, or is this just the
wrong description for this patch?

> ---
> mm/util.c | 26 ++++++++++++++++++++++++--
> 1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/mm/util.c b/mm/util.c
> index bab284d69c8c..992f0332dced 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -470,6 +470,28 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
> }
> EXPORT_SYMBOL(kvmalloc_node);
>
> +/**
> + * kvfree_fast() - Free memory.
> + * @addr: Pointer to allocated memory.
> + *
> + * kvfree_fast frees memory allocated by any of vmalloc(), kmalloc() or
> + * kvmalloc(). It is slightly more efficient to use kfree() or vfree() if
> + * you are certain that you know which one to use.
> + *
> + * Context: Either preemptible task context or not-NMI interrupt. Must not
> + * hold a spinlock as it can sleep.
> + */
> +void kvfree_fast(const void *addr)
> +{
> + might_sleep();
> +
> + if (is_vmalloc_addr(addr))
> + vfree(addr);
> + else
> + kfree(addr);
> +}
> +EXPORT_SYMBOL(kvfree_fast);
> +
> /**
> * kvfree() - Free memory.
> * @addr: Pointer to allocated memory.
> @@ -478,12 +500,12 @@ EXPORT_SYMBOL(kvmalloc_node);
> * It is slightly more efficient to use kfree() or vfree() if you are certain
> * that you know which one to use.
> *
> - * Context: Either preemptible task context or not-NMI interrupt.
> + * Context: Any context except NMI.
> */
> void kvfree(const void *addr)
> {
> if (is_vmalloc_addr(addr))
> - vfree(addr);
> + vfree_atomic(addr);
> else
> kfree(addr);
> }
> --
> 2.20.1
>

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