linux-kernel - [PATCH 3.16 10/99] padata: initialize pd->cpu with effective cpumask

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Message-ID: <lsq.1589984008.197502947@decadent.org.uk>
Date:   Wed, 20 May 2020 15:13:38 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Steffen Klassert" <steffen.klassert@...unet.com>,
        linux-crypto@...r.kernel.org,
        "Herbert Xu" <herbert@...dor.apana.org.au>,
        "Daniel Jordan" <daniel.m.jordan@...cle.com>
Subject: [PATCH 3.16 10/99] padata: initialize pd->cpu with effective cpumask

3.16.84-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Jordan <daniel.m.jordan@...cle.com>

commit ec9c7d19336ee98ecba8de80128aa405c45feebb upstream.

Exercising CPU hotplug on a 5.2 kernel with recent padata fixes from
cryptodev-2.6.git in an 8-CPU kvm guest...

    # modprobe tcrypt alg="pcrypt(rfc4106(gcm(aes)))" type=3
    # echo 0 > /sys/devices/system/cpu/cpu1/online
    # echo c > /sys/kernel/pcrypt/pencrypt/parallel_cpumask
    # modprobe tcrypt mode=215

...caused the following crash:

    BUG: kernel NULL pointer dereference, address: 0000000000000000
    #PF: supervisor read access in kernel mode
    #PF: error_code(0x0000) - not-present page
    PGD 0 P4D 0
    Oops: 0000 [#1] SMP PTI
    CPU: 2 PID: 134 Comm: kworker/2:2 Not tainted 5.2.0-padata-base+ #7
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-<snip>
    Workqueue: pencrypt padata_parallel_worker
    RIP: 0010:padata_reorder+0xcb/0x180
    ...
    Call Trace:
     padata_do_serial+0x57/0x60
     pcrypt_aead_enc+0x3a/0x50 [pcrypt]
     padata_parallel_worker+0x9b/0xe0
     process_one_work+0x1b5/0x3f0
     worker_thread+0x4a/0x3c0
     ...

In padata_alloc_pd, pd->cpu is set using the user-supplied cpumask
instead of the effective cpumask, and in this case cpumask_first picked
an offline CPU.

The offline CPU's reorder->list.next is NULL in padata_reorder because
the list wasn't initialized in padata_init_pqueues, which only operates
on CPUs in the effective mask.

Fix by using the effective mask in padata_alloc_pd.

Fixes: 6fc4dbcf0276 ("padata: Replace delayed timer with immediate workqueue in padata_reorder")
Signed-off-by: Daniel Jordan <daniel.m.jordan@...cle.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert@...unet.com>
Cc: linux-crypto@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/padata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -435,7 +435,7 @@ static struct parallel_data *padata_allo
 	atomic_set(&pd->refcnt, 0);
 	pd->pinst = pinst;
 	spin_lock_init(&pd->lock);
-	pd->cpu = cpumask_first(pcpumask);
+	pd->cpu = cpumask_first(pd->cpumask.pcpu);
 	INIT_WORK(&pd->reorder_work, invoke_padata_reorder);
 
 	return pd;