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Date: Mon, 9 Jun 2014 10:08:46 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: Mike Galbraith <umgwanakikbuti@...il.com>
CC: RT <linux-rt-users@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH] rt/aio: fix rcu garbage collection might_sleep()
splat
Hi, rt-people
I don't think it is the correct direction.
Softirq (including local_bh_disable()) in RT kernel should be preemptible.
Fixing these problems via converting spinlock_t to raw_spinlock_t will
result that all spinlock_t used in RCU-callbacks are converted which
means almost the spinlock_t in kernel are converted.
Sudden and superficial thought.
Thanks
Lai
On 06/08/2014 04:35 PM, Mike Galbraith wrote:
>
> [ 172.743098] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:768
> [ 172.743116] in_atomic(): 1, irqs_disabled(): 0, pid: 26, name: rcuos/2
> [ 172.743117] 2 locks held by rcuos/2/26:
> [ 172.743128] #0: (rcu_callback){.+.+..}, at: [<ffffffff810b1a12>] rcu_nocb_kthread+0x1e2/0x380
> [ 172.743135] #1: (rcu_read_lock_sched){.+.+..}, at: [<ffffffff812acd26>] percpu_ref_kill_rcu+0xa6/0x1c0
> [ 172.743138] Preemption disabled at:[<ffffffff810b1a93>] rcu_nocb_kthread+0x263/0x380
> [ 172.743138]
> [ 172.743142] CPU: 0 PID: 26 Comm: rcuos/2 Not tainted 3.14.4-rt5 #31
> [ 172.743143] Hardware name: MEDIONPC MS-7502/MS-7502, BIOS 6.00 PG 12/26/2007
> [ 172.743148] ffff8802231aa190 ffff8802231a5d08 ffffffff81582e9e 0000000000000000
> [ 172.743151] ffff8802231a5d28 ffffffff81077aeb ffff880209f68140 ffff880209f681c0
> [ 172.743154] ffff8802231a5d48 ffffffff81589304 ffff880209f68000 ffff880209f68000
> [ 172.743155] Call Trace:
> [ 172.743160] [<ffffffff81582e9e>] dump_stack+0x4e/0x9c
> [ 172.743163] [<ffffffff81077aeb>] __might_sleep+0xfb/0x170
> [ 172.743167] [<ffffffff81589304>] rt_spin_lock+0x24/0x70
> [ 172.743171] [<ffffffff811c5790>] free_ioctx_users+0x30/0x130
> [ 172.743174] [<ffffffff812ace34>] percpu_ref_kill_rcu+0x1b4/0x1c0
> [ 172.743177] [<ffffffff812acd26>] ? percpu_ref_kill_rcu+0xa6/0x1c0
> [ 172.743180] [<ffffffff812acc80>] ? percpu_ref_kill_and_confirm+0x70/0x70
> [ 172.743183] [<ffffffff810b1a93>] rcu_nocb_kthread+0x263/0x380
> [ 172.743185] [<ffffffff810b1a12>] ? rcu_nocb_kthread+0x1e2/0x380
> [ 172.743189] [<ffffffff810b1830>] ? rcu_report_exp_rnp.isra.52+0xc0/0xc0
> [ 172.743192] [<ffffffff8106e046>] kthread+0xd6/0xf0
> [ 172.743194] [<ffffffff8158900c>] ? _raw_spin_unlock_irq+0x2c/0x70
> [ 172.743197] [<ffffffff8106df70>] ? __kthread_parkme+0x70/0x70
> [ 172.743200] [<ffffffff81591eec>] ret_from_fork+0x7c/0xb0
> [ 172.743203] [<ffffffff8106df70>] ? __kthread_parkme+0x70/0x70
>
> crash> gdb list *percpu_ref_kill_rcu+0x1b4
> 0xffffffff812ace34 is in percpu_ref_kill_rcu (include/linux/percpu-refcount.h:169).
> 164 pcpu_count = ACCESS_ONCE(ref->pcpu_count);
> 165
> 166 if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR))
> 167 __this_cpu_dec(*pcpu_count);
> 168 else if (unlikely(atomic_dec_and_test(&ref->count)))
> 169 ref->release(ref);
> 170
> 171 rcu_read_unlock_sched();
> 172 }
> 173
>
> Ok, so ->release() can't do anything where it may meet a sleeping lock,
> but in an -rt kernel, it does that.
>
> Convert struct kioctx ctx_lock/completion_lock to raw_spinlock_t, and
> defer final free to a time when we're not under rcu_read_lock_sched().
>
> runltp -f ltp-aio-stress.part1 runs kernel/ltp gripe free.
>
> INFO: ltp-pan reported all tests PASS
> LTP Version: 20140422
>
> ###############################################################
>
> Done executing testcases.
> LTP Version: 20140422
> ###############################################################
>
>
> Signed-off-by: Mike Galbraith <umgwanakikbuti@...il.com>
> ---
> fs/aio.c | 61 ++++++++++++++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 44 insertions(+), 17 deletions(-)
>
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -125,7 +125,7 @@ struct kioctx {
> } ____cacheline_aligned_in_smp;
>
> struct {
> - spinlock_t ctx_lock;
> + raw_spinlock_t ctx_lock;
> struct list_head active_reqs; /* used for cancellation */
> } ____cacheline_aligned_in_smp;
>
> @@ -136,13 +136,16 @@ struct kioctx {
>
> struct {
> unsigned tail;
> - spinlock_t completion_lock;
> + raw_spinlock_t completion_lock;
> } ____cacheline_aligned_in_smp;
>
> struct page *internal_pages[AIO_RING_PAGES];
> struct file *aio_ring_file;
>
> unsigned id;
> +#ifdef CONFIG_PREEMPT_RT_BASE
> + struct rcu_head rcu;
> +#endif
> };
>
> /*------ sysctl variables----*/
> @@ -334,11 +337,11 @@ static int aio_migratepage(struct addres
> * while the old page is copied to the new. This prevents new
> * events from being lost.
> */
> - spin_lock_irqsave(&ctx->completion_lock, flags);
> + raw_spin_lock_irqsave(&ctx->completion_lock, flags);
> migrate_page_copy(new, old);
> BUG_ON(ctx->ring_pages[idx] != old);
> ctx->ring_pages[idx] = new;
> - spin_unlock_irqrestore(&ctx->completion_lock, flags);
> + raw_spin_unlock_irqrestore(&ctx->completion_lock, flags);
>
> /* The old page is no longer accessible. */
> put_page(old);
> @@ -461,14 +464,14 @@ void kiocb_set_cancel_fn(struct kiocb *r
> struct kioctx *ctx = req->ki_ctx;
> unsigned long flags;
>
> - spin_lock_irqsave(&ctx->ctx_lock, flags);
> + raw_spin_lock_irqsave(&ctx->ctx_lock, flags);
>
> if (!req->ki_list.next)
> list_add(&req->ki_list, &ctx->active_reqs);
>
> req->ki_cancel = cancel;
>
> - spin_unlock_irqrestore(&ctx->ctx_lock, flags);
> + raw_spin_unlock_irqrestore(&ctx->ctx_lock, flags);
> }
> EXPORT_SYMBOL(kiocb_set_cancel_fn);
>
> @@ -493,6 +496,7 @@ static int kiocb_cancel(struct kioctx *c
> return cancel(kiocb);
> }
>
> +#ifndef CONFIG_PREEMPT_RT_BASE
> static void free_ioctx(struct work_struct *work)
> {
> struct kioctx *ctx = container_of(work, struct kioctx, free_work);
> @@ -503,13 +507,36 @@ static void free_ioctx(struct work_struc
> free_percpu(ctx->cpu);
> kmem_cache_free(kioctx_cachep, ctx);
> }
> +#else
> +static void free_ioctx_rcu(struct rcu_head *rcu)
> +{
> + struct kioctx *ctx = container_of(rcu, struct kioctx, rcu);
> +
> + pr_debug("freeing %p\n", ctx);
> +
> + aio_free_ring(ctx);
> + free_percpu(ctx->cpu);
> + kmem_cache_free(kioctx_cachep, ctx);
> +}
> +#endif
>
> static void free_ioctx_reqs(struct percpu_ref *ref)
> {
> struct kioctx *ctx = container_of(ref, struct kioctx, reqs);
>
> +#ifndef CONFIG_PREEMPT_RT_BASE
> INIT_WORK(&ctx->free_work, free_ioctx);
> schedule_work(&ctx->free_work);
> +#else
> + /*
> + * We're in ->release() under rcu_read_lock_sched(), and can't do
> + * anything that requires taking a sleeping lock, so ->release()
> + * becomes a two stage rcu process for -rt. We've now done the
> + * rcu work that we can under locks made raw to get us this far.
> + * Defer the freeing bit until we're again allowed to schedule().
> + */
> + call_rcu(&ctx->rcu, free_ioctx_rcu);
> +#endif
> }
>
> /*
> @@ -522,7 +549,7 @@ static void free_ioctx_users(struct perc
> struct kioctx *ctx = container_of(ref, struct kioctx, users);
> struct kiocb *req;
>
> - spin_lock_irq(&ctx->ctx_lock);
> + raw_spin_lock_irq(&ctx->ctx_lock);
>
> while (!list_empty(&ctx->active_reqs)) {
> req = list_first_entry(&ctx->active_reqs,
> @@ -532,7 +559,7 @@ static void free_ioctx_users(struct perc
> kiocb_cancel(ctx, req);
> }
>
> - spin_unlock_irq(&ctx->ctx_lock);
> + raw_spin_unlock_irq(&ctx->ctx_lock);
>
> percpu_ref_kill(&ctx->reqs);
> percpu_ref_put(&ctx->reqs);
> @@ -645,8 +672,8 @@ static struct kioctx *ioctx_alloc(unsign
>
> ctx->max_reqs = nr_events;
>
> - spin_lock_init(&ctx->ctx_lock);
> - spin_lock_init(&ctx->completion_lock);
> + raw_spin_lock_init(&ctx->ctx_lock);
> + raw_spin_lock_init(&ctx->completion_lock);
> mutex_init(&ctx->ring_lock);
> /* Protect against page migration throughout kiotx setup by keeping
> * the ring_lock mutex held until setup is complete. */
> @@ -948,9 +975,9 @@ void aio_complete(struct kiocb *iocb, lo
> if (iocb->ki_list.next) {
> unsigned long flags;
>
> - spin_lock_irqsave(&ctx->ctx_lock, flags);
> + raw_spin_lock_irqsave(&ctx->ctx_lock, flags);
> list_del(&iocb->ki_list);
> - spin_unlock_irqrestore(&ctx->ctx_lock, flags);
> + raw_spin_unlock_irqrestore(&ctx->ctx_lock, flags);
> }
>
> /*
> @@ -958,7 +985,7 @@ void aio_complete(struct kiocb *iocb, lo
> * ctx->completion_lock to prevent other code from messing with the tail
> * pointer since we might be called from irq context.
> */
> - spin_lock_irqsave(&ctx->completion_lock, flags);
> + raw_spin_lock_irqsave(&ctx->completion_lock, flags);
>
> tail = ctx->tail;
> pos = tail + AIO_EVENTS_OFFSET;
> @@ -993,7 +1020,7 @@ void aio_complete(struct kiocb *iocb, lo
> kunmap_atomic(ring);
> flush_dcache_page(ctx->ring_pages[0]);
>
> - spin_unlock_irqrestore(&ctx->completion_lock, flags);
> + raw_spin_unlock_irqrestore(&ctx->completion_lock, flags);
>
> pr_debug("added to ring %p at [%u]\n", iocb, tail);
>
> @@ -1515,7 +1542,7 @@ static struct kiocb *lookup_kiocb(struct
> {
> struct list_head *pos;
>
> - assert_spin_locked(&ctx->ctx_lock);
> + assert_raw_spin_locked(&ctx->ctx_lock);
>
> if (key != KIOCB_KEY)
> return NULL;
> @@ -1555,7 +1582,7 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t
> if (unlikely(!ctx))
> return -EINVAL;
>
> - spin_lock_irq(&ctx->ctx_lock);
> + raw_spin_lock_irq(&ctx->ctx_lock);
>
> kiocb = lookup_kiocb(ctx, iocb, key);
> if (kiocb)
> @@ -1563,7 +1590,7 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t
> else
> ret = -EINVAL;
>
> - spin_unlock_irq(&ctx->ctx_lock);
> + raw_spin_unlock_irq(&ctx->ctx_lock);
>
> if (!ret) {
> /*
>
>
> --
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