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Message-ID: <20180928164108.GE21895@zn.tnic>
Date: Fri, 28 Sep 2018 18:41:08 +0200
From: Borislav Petkov <bp@...e.de>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: linux-kernel@...r.kernel.org, Lianbo Jiang <lijiang@...hat.com>,
Vivek Goyal <vgoyal@...hat.com>, kexec@...ts.infradead.org,
tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
x86@...nel.org, akpm@...ux-foundation.org,
dan.j.williams@...el.com, thomas.lendacky@....com,
baiyaowei@...s.chinamobile.com, tiwai@...e.de,
brijesh.singh@....com, dyoung@...hat.com, bhe@...hat.com
Subject: Re: [PATCH 3/3] resource: Fix find_next_iomem_res() iteration issue
On Thu, Sep 27, 2018 at 09:22:09AM -0500, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
>
> Previously find_next_iomem_res() used "*res" as both an input parameter for
> the range to search and the type of resource to search for, and an output
> parameter for the resource we found, which makes the interface confusing.
>
> The current callers use find_next_iomem_res() incorrectly because they
> allocate a single struct resource and use it for repeated calls to
> find_next_iomem_res(). When find_next_iomem_res() returns a resource, it
> overwrites the start, end, flags, and desc members of the struct. If we
> call find_next_iomem_res() again, we must update or restore these fields.
> The previous code restored res.start and res.end, but not res.flags or
> res.desc.
... which is a sure sign that the design of this thing is not the best one.
>
> Since the callers did not restore res.flags, if they searched for flags
> IORESOURCE_MEM | IORESOURCE_BUSY and found a resource with flags
> IORESOURCE_MEM | IORESOURCE_BUSY | IORESOURCE_SYSRAM, the next search would
> incorrectly skip resources unless they were also marked as
> IORESOURCE_SYSRAM.
Nice example!
> Fix this by restructuring the interface so it takes explicit "start, end,
> flags" parameters and uses "*res" only as an output parameter.
>
> Original-patch: http://lore.kernel.org/lkml/20180921073211.20097-2-lijiang@redhat.com
> Based-on-patch-by: Lianbo Jiang <lijiang@...hat.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
> kernel/resource.c | 94 +++++++++++++++++++++++------------------------------
> 1 file changed, 41 insertions(+), 53 deletions(-)
>
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 155ec873ea4d..9891ea90cc8f 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -319,23 +319,26 @@ int release_resource(struct resource *old)
> EXPORT_SYMBOL(release_resource);
>
> /*
I guess this could be made kernel-doc, since you're touching it...
> - * Finds the lowest iomem resource existing within [res->start..res->end].
> - * The caller must specify res->start, res->end, res->flags, and optionally
> - * desc. If found, returns 0, res is overwritten, if not found, returns -1.
> - * This function walks the whole tree and not just first level children until
> - * and unless first_level_children_only is true.
> + * Finds the lowest iomem resource that covers part of [start..end]. The
> + * caller must specify start, end, flags, and desc (which may be
> + * IORES_DESC_NONE).
> + *
> + * If a resource is found, returns 0 and *res is overwritten with the part
> + * of the resource that's within [start..end]; if none is found, returns
> + * -1.
> + *
> + * This function walks the whole tree and not just first level children
> + * unless first_level_children_only is true.
... and then prepend that with '@' - @first_level_children_only to refer
to the function parameter.
> */
> -static int find_next_iomem_res(struct resource *res, unsigned long desc,
> - bool first_level_children_only)
> +static int find_next_iomem_res(resource_size_t start, resource_size_t end,
> + unsigned long flags, unsigned long desc,
> + bool first_level_children_only,
> + struct resource *res)
> {
> - resource_size_t start, end;
> struct resource *p;
> bool sibling_only = false;
>
> BUG_ON(!res);
> -
> - start = res->start;
> - end = res->end;
> BUG_ON(start >= end);
And since we're touching this, maybe replace that BUG_ON() fun with
simply return -EINVAL or some error code...
>
> if (first_level_children_only)
if (first_level_children_only)
sibling_only = true;
So this is just silly - replacing a bool function param with a local bool
var.
You could kill that, shorten first_level_children_only's name and use it
directly.
Depending on how much cleanup it amounts to, you could make that a
separate cleanup patch ontop, to keep the changes from the cleanup
separate.
> @@ -344,7 +347,7 @@ static int find_next_iomem_res(struct resource *res, unsigned long desc,
> read_lock(&resource_lock);
>
> for (p = iomem_resource.child; p; p = next_resource(p, sibling_only)) {
> - if ((p->flags & res->flags) != res->flags)
> + if ((p->flags & flags) != flags)
> continue;
> if ((desc != IORES_DESC_NONE) && (desc != p->desc))
> continue;
> @@ -359,32 +362,31 @@ static int find_next_iomem_res(struct resource *res, unsigned long desc,
> read_unlock(&resource_lock);
> if (!p)
> return -1;
> +
> /* copy data */
> - if (res->start < p->start)
> - res->start = p->start;
> - if (res->end > p->end)
> - res->end = p->end;
> + res->start = max(start, p->start);
> + res->end = min(end, p->end);
Should we use the min_t and max_t versions here for typechecking?
> res->flags = p->flags;
> res->desc = p->desc;
> return 0;
> }
>
> -static int __walk_iomem_res_desc(struct resource *res, unsigned long desc,
> - bool first_level_children_only,
> - void *arg,
> +static int __walk_iomem_res_desc(resource_size_t start, resource_size_t end,
> + unsigned long flags, unsigned long desc,
> + bool first_level_children_only, void *arg,
> int (*func)(struct resource *, void *))
> {
> - u64 orig_end = res->end;
> + struct resource res;
> int ret = -1;
>
> - while ((res->start < res->end) &&
> - !find_next_iomem_res(res, desc, first_level_children_only)) {
> - ret = (*func)(res, arg);
> + while (start < end &&
> + !find_next_iomem_res(start, end, flags, desc,
> + first_level_children_only, &res)) {
> + ret = (*func)(&res, arg);
> if (ret)
> break;
>
> - res->start = res->end + 1;
> - res->end = orig_end;
> + start = res.end + 1;
> }
>
> return ret;
> @@ -407,13 +409,7 @@ static int __walk_iomem_res_desc(struct resource *res, unsigned long desc,
> int walk_iomem_res_desc(unsigned long desc, unsigned long flags, u64 start,
> u64 end, void *arg, int (*func)(struct resource *, void *))
Align that function's parameters on the opening brace, pls, while you're
at it.
> {
> - struct resource res;
> -
> - res.start = start;
> - res.end = end;
> - res.flags = flags;
> -
> - return __walk_iomem_res_desc(&res, desc, false, arg, func);
> + return __walk_iomem_res_desc(start, end, flags, desc, false, arg, func);
> }
> EXPORT_SYMBOL_GPL(walk_iomem_res_desc);
>
> @@ -427,13 +423,9 @@ EXPORT_SYMBOL_GPL(walk_iomem_res_desc);
> int walk_system_ram_res(u64 start, u64 end, void *arg,
> int (*func)(struct resource *, void *))
Ditto.
> {
> - struct resource res;
> -
> - res.start = start;
> - res.end = end;
> - res.flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> + unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>
> - return __walk_iomem_res_desc(&res, IORES_DESC_NONE, true,
> + return __walk_iomem_res_desc(start, end, flags, IORES_DESC_NONE, true,
> arg, func);
> }
>
> @@ -444,13 +436,9 @@ int walk_system_ram_res(u64 start, u64 end, void *arg,
> int walk_mem_res(u64 start, u64 end, void *arg,
> int (*func)(struct resource *, void *))
> {
> - struct resource res;
> -
> - res.start = start;
> - res.end = end;
> - res.flags = IORESOURCE_MEM | IORESOURCE_BUSY;
> + unsigned long flags = IORESOURCE_MEM | IORESOURCE_BUSY;
>
> - return __walk_iomem_res_desc(&res, IORES_DESC_NONE, true,
> + return __walk_iomem_res_desc(start, end, flags, IORES_DESC_NONE, true,
> arg, func);
> }
>
> @@ -464,25 +452,25 @@ int walk_mem_res(u64 start, u64 end, void *arg,
> int walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
> void *arg, int (*func)(unsigned long, unsigned long, void *))
Ditto.
With that addressed:
Reviewed-by: Borislav Petkov <bp@...e.de>
All good stuff and a charm to review, lemme know if I should take them
or you can carry them.
Thanks!
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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