lkml.org 
[lkml]   [2019]   [Aug]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2 1/5] padata: make flushing work with async users
Date
padata_flush_queues() is broken for an async ->parallel() function
because flush_work() can't wait on it:

# modprobe tcrypt alg="pcrypt(cryptd(rfc4106(gcm_base(ctr(aes-generic),ghash-generic))))" type=3
# modprobe tcrypt mode=215 sec=1 &
# sleep 5; echo 7 > /sys/kernel/pcrypt/pencrypt/parallel_cpumask

kernel BUG at kernel/padata.c:473!
invalid opcode: 0000 [#1] SMP PTI
CPU: 0 PID: 282 Comm: sh Not tainted 5.3.0-rc5-padata-base+ #3
RIP: 0010:padata_flush_queues+0xa7/0xb0
Call Trace:
padata_replace+0xa1/0x110
padata_set_cpumask+0xae/0x130
store_cpumask+0x75/0xa0
padata_sysfs_store+0x20/0x30
...

Wait instead for the parallel_data (pd) object's refcount to drop to
zero.

Simplify by taking an initial reference on a pd when allocating an
instance. That ref is dropped during flushing, which allows calling
wait_for_completion() unconditionally.

If the initial ref weren't used, the only other alternative I could
think of is that complete() would be conditional on !PADATA_INIT or
PADATA_REPLACE (in addition to zero pd->refcnt), and
wait_for_completion() on nonzero pd->refcnt. But then complete() could
be called without a matching wait:

completer waiter
--------- ------
DEC pd->refcnt // 0
pinst->flags |= PADATA_REPLACE
LOAD pinst->flags // REPLACE
LOAD pd->refcnt // 0
/* return without wait_for_completion() */
complete()

No more flushing per-CPU work items, so no more CPU hotplug lock in
__padata_stop.

Fixes: 2b73b07ab8a4 ("padata: Flush the padata queues actively")
Reported-by: Herbert Xu <herbert@gondor.apana.org.au>
Suggested-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
include/linux/padata.h | 3 +++
kernel/padata.c | 32 ++++++++++++--------------------
2 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/include/linux/padata.h b/include/linux/padata.h
index 8da673861d99..1c73f9cc7b72 100644
--- a/include/linux/padata.h
+++ b/include/linux/padata.h
@@ -14,6 +14,7 @@
#include <linux/list.h>
#include <linux/notifier.h>
#include <linux/kobject.h>
+#include <linux/completion.h>

#define PADATA_CPU_SERIAL 0x01
#define PADATA_CPU_PARALLEL 0x02
@@ -104,6 +105,7 @@ struct padata_cpumask {
* @squeue: percpu padata queues used for serialuzation.
* @reorder_objects: Number of objects waiting in the reorder queues.
* @refcnt: Number of objects holding a reference on this parallel_data.
+ * @flushing_done: Wait for all objects to be sent out.
* @max_seq_nr: Maximal used sequence number.
* @cpu: Next CPU to be processed.
* @cpumask: The cpumasks in use for parallel and serial workers.
@@ -116,6 +118,7 @@ struct parallel_data {
struct padata_serial_queue __percpu *squeue;
atomic_t reorder_objects;
atomic_t refcnt;
+ struct completion flushing_done;
atomic_t seq_nr;
int cpu;
struct padata_cpumask cpumask;
diff --git a/kernel/padata.c b/kernel/padata.c
index b60cc3dcee58..958166e23123 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -301,7 +301,8 @@ static void padata_serial_worker(struct work_struct *serial_work)
list_del_init(&padata->list);

padata->serial(padata);
- atomic_dec(&pd->refcnt);
+ if (atomic_dec_return(&pd->refcnt) == 0)
+ complete(&pd->flushing_done);
}
local_bh_enable();
}
@@ -423,7 +424,9 @@ static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst,
padata_init_squeues(pd);
atomic_set(&pd->seq_nr, -1);
atomic_set(&pd->reorder_objects, 0);
- atomic_set(&pd->refcnt, 0);
+ /* Initial ref dropped in padata_flush_queues. */
+ atomic_set(&pd->refcnt, 1);
+ init_completion(&pd->flushing_done);
pd->pinst = pinst;
spin_lock_init(&pd->lock);
pd->cpu = cpumask_first(pd->cpumask.pcpu);
@@ -453,24 +456,15 @@ static void padata_free_pd(struct parallel_data *pd)
/* Flush all objects out of the padata queues. */
static void padata_flush_queues(struct parallel_data *pd)
{
- int cpu;
- struct padata_parallel_queue *pqueue;
- struct padata_serial_queue *squeue;
-
- for_each_cpu(cpu, pd->cpumask.pcpu) {
- pqueue = per_cpu_ptr(pd->pqueue, cpu);
- flush_work(&pqueue->work);
- }
-
- if (atomic_read(&pd->reorder_objects))
- padata_reorder(pd);
+ if (!(pd->pinst->flags & PADATA_INIT))
+ return;

- for_each_cpu(cpu, pd->cpumask.cbcpu) {
- squeue = per_cpu_ptr(pd->squeue, cpu);
- flush_work(&squeue->work);
- }
+ if (atomic_dec_return(&pd->refcnt) == 0)
+ complete(&pd->flushing_done);

- BUG_ON(atomic_read(&pd->refcnt) != 0);
+ wait_for_completion(&pd->flushing_done);
+ reinit_completion(&pd->flushing_done);
+ atomic_set(&pd->refcnt, 1);
}

static void __padata_start(struct padata_instance *pinst)
@@ -487,9 +481,7 @@ static void __padata_stop(struct padata_instance *pinst)

synchronize_rcu();

- get_online_cpus();
padata_flush_queues(pinst->pd);
- put_online_cpus();
}

/* Replace the internal control structure with a new one. */
--
2.23.0
\
 
 \ /
  Last update: 2019-08-29 00:19    [W:0.115 / U:0.776 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site