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Message-ID: <de1201930a55aa3b13f413b9bee986d85e2b4283.camel@redhat.com>
Date: Fri, 29 Nov 2024 11:12:52 -0500
From: Radu Rendec <rrendec@...hat.com>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>, x86@...nel.org
Cc: Andreas Herrmann <aherrmann@...e.com>, Catalin Marinas
<catalin.marinas@....com>, Chen Yu <yu.c.chen@...el.com>, Len Brown
<len.brown@...el.com>, Pierre Gondois <Pierre.Gondois@....com>, Pu Wen
<puwen@...on.cn>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Sudeep
Holla <sudeep.holla@....com>, Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com>, Will Deacon <will@...nel.org>,
Zhang Rui <rui.zhang@...el.com>, Nikolay Borisov <nik.borisov@...e.com>,
Huang Ying <ying.huang@...el.com>, Ricardo Neri <ricardo.neri@...el.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 1/2] cacheinfo: Allocate memory during CPU hotplug if
not done from the primary CPU
On Wed, 2024-11-27 at 16:22 -0800, Ricardo Neri wrote:
> Commit 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")
> adds functionality that architectures can use to optionally allocate and
> build cacheinfo early during boot. Commit 6539cffa9495 ("cacheinfo: Add
> arch specific early level initializer") lets secondary CPUs correct (and
> reallocate memory) cacheinfo data if needed.
>
> If the early build functionality is not used and cacheinfo does not need
> correction, memory for cacheinfo is never allocated. x86 does not use the
> early build functionality. Consequently, during the cacheinfo CPU hotplug
> callback, last_level_cache_is_valid() attempts to dereference a NULL
> pointer:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000100
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not present page
> PGD 0 P4D 0
> Oops: 0000 [#1] PREEPMT SMP NOPTI
> CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1
> RIP: 0010: last_level_cache_is_valid+0x95/0xe0a
>
> Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback if
> not done earlier.
>
> Moreover, before determining the validity of the last-level cache info,
> ensure that it has been allocated. Simply checking for non-zero
> cache_leaves() is not sufficient, as some architectures (e.g., Intel
> processors) have non-zero cache_leaves() before allocation.
>
> Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size().
> This function iterates over all online CPUs. However, a CPU may have come
> online recently, but its cacheinfo may not have been allocated yet.
>
> While here, remove an unnecessary indentation in allocate_cache_info().
>
> Reviewed-by: Andreas Herrmann <aherrmann@...e.de>
> Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>
> Reviewed-by: Radu Rendec <rrendec@...hat.com>
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> Tested-by: Andreas Herrmann <aherrmann@...e.de>
> Fixes: 6539cffa9495 ("cacheinfo: Add arch specific early level initializer")
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
> Cc: Andreas Herrmann <aherrmann@...e.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Chen Yu <yu.c.chen@...el.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Nikolay Borisov <nik.borisov@...e.com>
> Cc: Radu Rendec <rrendec@...hat.com>
> Cc: Pierre Gondois <Pierre.Gondois@....com>
> Cc: Pu Wen <puwen@...on.cn>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
> Cc: Sudeep Holla <sudeep.holla@....com>
> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Zhang Rui <rui.zhang@...el.com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: stable@...r.kernel.org # 6.3+
> ---
> Change since v7:
> * None
>
> Changes since v6:
> * Merged patches 1 and 2 of v6 into one. (Borislav)
> * Merged the history of patches 1 and 2ino this patch.
> * Kept the Reviewed-by and Tested-by tags from the two merged patches.
> * Fixed a formatting issue in allocate_cache_info(). (Borislav)
>
> Changes since v5:
> * Fixed nonsensical subject (Nikolay).
> * Added Reviewed-by and Tested-by tags from Andreas. Thanks!
> * Added Reviewed-by tag from Nikolay. Thanks!
>
> Changes since v4:
> * Combined checks for per_cpu_cacheinfo() and cache_leaves() in a single
> line. (Sudeep)
> * Added Reviewed-by tag from Sudeep. Thanks!
>
> Changes since v3:
> * Added Reviewed-by tag from Radu and Sudeep. Thanks!
>
> Changes since v2:
> * Introduced this patch.
>
> Changes since v1:
> * N/A
>
> ---
> The motivation for commit 5944ce092b97 was to prevent a BUG splat in
> PREEMPT_RT kernels during memory allocation. This splat is not observed on
> x86 because the memory allocation for cacheinfo happens in
> detect_cache_attributes() from the cacheinfo CPU hotplug callback.
>
> The dereference of a NULL cacheinfo is not observed today because
> cache_leaves(cpu) is zero until after init_cache_level() is called
> (during the CPU hotplug callback). A subsequent changeset will set
> the number of cache leaves earlier and the NULL-pointer dereference
> will be observed.
> ---
> drivers/base/cacheinfo.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> index 7a7609298e18..a1afc478e0e8 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -58,7 +58,7 @@ bool last_level_cache_is_valid(unsigned int cpu)
> {
> struct cacheinfo *llc;
>
> - if (!cache_leaves(cpu))
> + if (!cache_leaves(cpu) || !per_cpu_cacheinfo(cpu))
> return false;
>
> llc = per_cpu_cacheinfo_idx(cpu, cache_leaves(cpu) - 1);
> @@ -466,8 +466,7 @@ int __weak populate_cache_leaves(unsigned int cpu)
> static inline
> int allocate_cache_info(int cpu)
> {
> - per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu),
> - sizeof(struct cacheinfo), GFP_ATOMIC);
> + per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu), sizeof(struct cacheinfo), GFP_ATOMIC);
> if (!per_cpu_cacheinfo(cpu)) {
> cache_leaves(cpu) = 0;
> return -ENOMEM;
> @@ -539,7 +538,11 @@ static inline int init_level_allocate_ci(unsigned int cpu)
> */
> ci_cacheinfo(cpu)->early_ci_levels = false;
>
> - if (cache_leaves(cpu) <= early_leaves)
> + /*
> + * Some architectures (e.g., x86) do not use early initialization.
> + * Allocate memory now in such case.
> + */
> + if (cache_leaves(cpu) <= early_leaves && per_cpu_cacheinfo(cpu))
> return 0;
>
> kfree(per_cpu_cacheinfo(cpu));
Since Borislav explicitly said you were not supposed to keep the tags,
I reviewed it again, and I'm OK to keep mine. Thanks!
Reviewed-by: Radu Rendec <rrendec@...hat.com>
--
Best regards,
Radu
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