[PATCH v2 0/2] Fix warnings in blktrace

[PATCH v2 0/2] Fix warnings in blktrace

[Wander Lairson Costa]

These two patches fix wrong usage of lock primitives with
CONFIG_PREEMPT_RT in the blktrace code.

This version fixes a missing piece in the blktrace patch.

The patches apply to the PREEMPT_RT tree.

Wander Lairson Costa (2):
  block: Avoid sleeping function called from invalid context bug
  blktrace: switch trace spinlock to a raw spinlock

 block/blk-cgroup.c      |  4 ++--
 kernel/trace/blktrace.c | 18 +++++++++---------
 2 files changed, 11 insertions(+), 11 deletions(-)

-- 
2.27.0

[PATCH v2 1/2] block: Avoid sleeping function called from invalid context bug

[Wander Lairson Costa]

This was caught during QA test:

 BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:942
 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 243401, name: sed
 INFO: lockdep is turned off.
 Preemption disabled at:
 [<ffffffff89b26268>] blk_cgroup_bio_start+0x28/0xd0

 CPU: 2 PID: 243401 Comm: sed Kdump: loaded Not tainted 4.18.0-353.rt7.138.el8.x86_64+debug #1
 Hardware name: HP ProLiant DL380 Gen9, BIOS P89 05/06/2015
 Call Trace:
  dump_stack+0x5c/0x80
  ___might_sleep.cold.89+0xf5/0x109
  rt_spin_lock+0x3e/0xd0
  ? __blk_add_trace+0x428/0x4b0
  __blk_add_trace+0x428/0x4b0
  blk_add_trace_bio+0x16e/0x1c0
  generic_make_request_checks+0x7e8/0x8c0
  generic_make_request+0x3c/0x420
  ? membarrier_private_expedited+0xd0/0x2b0
  ? lock_release+0x1ca/0x450
  ? submit_bio+0x3c/0x160
  ? _raw_spin_unlock_irqrestore+0x3c/0x80
  submit_bio+0x3c/0x160
  ? rt_mutex_futex_unlock+0x66/0xa0
  iomap_submit_ioend.isra.36+0x4a/0x70
  xfs_vm_writepages+0x65/0x90 [xfs]
  do_writepages+0x41/0xe0
  ? rt_mutex_futex_unlock+0x66/0xa0
  __filemap_fdatawrite_range+0xce/0x110
  xfs_release+0x11c/0x160 [xfs]
  __fput+0xd5/0x270
  task_work_run+0xa1/0xd0
  exit_to_usermode_loop+0x14d/0x160
  do_syscall_64+0x23b/0x240
  entry_SYSCALL_64_after_hwframe+0x6a/0xdf

We replace the get/put_cpu() call by get/put_cpu_light to avoid this bug.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
---
 block/blk-cgroup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 663aabfeba18..0a532bb3003c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1911,7 +1911,7 @@ void blk_cgroup_bio_start(struct bio *bio)
 	struct blkg_iostat_set *bis;
 	unsigned long flags;
 
-	cpu = get_cpu();
+	cpu = get_cpu_light();
 	bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
 	flags = u64_stats_update_begin_irqsave(&bis->sync);
 
@@ -1928,7 +1928,7 @@ void blk_cgroup_bio_start(struct bio *bio)
 	u64_stats_update_end_irqrestore(&bis->sync, flags);
 	if (cgroup_subsys_on_dfl(io_cgrp_subsys))
 		cgroup_rstat_updated(bio->bi_blkg->blkcg->css.cgroup, cpu);
-	put_cpu();
+	put_cpu_light();
 }
 
 static int __init blkcg_init(void)
-- 
2.27.0

[PATCH v2 2/2] blktrace: switch trace spinlock to a raw spinlock

[Wander Lairson Costa]

TRACE_EVENT disables preemption before calling the callback. Because of
that blktrace triggers the following bug under PREEMPT_RT:

 BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:35
 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 119, name: kworker/u2:2
 5 locks held by kworker/u2:2/119:
  #0: ffff8c2e4a88f538 ((wq_completion)xfs-cil/dm-0){+.+.}-{0:0}, at: process_one_work+0x200/0x450
  #1: ffffab3840ac7e68 ((work_completion)(&cil->xc_push_work)){+.+.}-{0:0}, at: process_one_work+0x200/0x450
  #2: ffff8c2e4a887128 (&cil->xc_ctx_lock){++++}-{3:3}, at: xlog_cil_push_work+0xb7/0x670 [xfs]
  #3: ffffffffa6a63780 (rcu_read_lock){....}-{1:2}, at: blk_add_trace_bio+0x0/0x1f0
  #4: ffffffffa6610620 (running_trace_lock){+.+.}-{2:2}, at: __blk_add_trace+0x3ef/0x480
 Preemption disabled at:
 [<ffffffffa4d35c05>] migrate_enable+0x45/0x140
 CPU: 0 PID: 119 Comm: kworker/u2:2 Kdump: loaded Not tainted 5.14.0-25.rt21.25.light.el9.x86_64+debug #1
 Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
 Workqueue: xfs-cil/dm-0 xlog_cil_push_work [xfs]
 Call Trace:
  ? migrate_enable+0x45/0x140
  dump_stack_lvl+0x57/0x7d
  ___might_sleep.cold+0xe3/0xf7
  rt_spin_lock+0x3a/0xd0
  ? __blk_add_trace+0x3ef/0x480
  __blk_add_trace+0x3ef/0x480
  blk_add_trace_bio+0x18d/0x1f0
  trace_block_bio_queue+0xb5/0x150
  submit_bio_checks+0x1f0/0x520
  ? sched_clock_cpu+0xb/0x100
  submit_bio_noacct+0x30/0x1d0
  ? bio_associate_blkg+0x66/0x190
  xlog_cil_push_work+0x1b6/0x670 [xfs]
  ? register_lock_class+0x43/0x4f0
  ? xfs_swap_extents+0x5f0/0x5f0 [xfs]
  process_one_work+0x275/0x450
  ? process_one_work+0x200/0x450
  worker_thread+0x55/0x3c0
  ? process_one_work+0x450/0x450
  kthread+0x188/0x1a0
  ? set_kthread_struct+0x40/0x40
  ret_from_fork+0x22/0x30

To avoid this bug, we switch the trace lock to a raw spinlock.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
---
 kernel/trace/blktrace.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 1183c88634aa..a86e022f7155 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -34,7 +34,7 @@ static struct trace_array *blk_tr;
 static bool blk_tracer_enabled __read_mostly;
 
 static LIST_HEAD(running_trace_list);
-static __cacheline_aligned_in_smp DEFINE_SPINLOCK(running_trace_lock);
+static __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(running_trace_lock);
 
 /* Select an alternative, minimalistic output than the original one */
 #define TRACE_BLK_OPT_CLASSIC	0x1
@@ -121,12 +121,12 @@ static void trace_note_tsk(struct task_struct *tsk)
 	struct blk_trace *bt;
 
 	tsk->btrace_seq = blktrace_seq;
-	spin_lock_irqsave(&running_trace_lock, flags);
+	raw_spin_lock_irqsave(&running_trace_lock, flags);
 	list_for_each_entry(bt, &running_trace_list, running_list) {
 		trace_note(bt, tsk->pid, BLK_TN_PROCESS, tsk->comm,
 			   sizeof(tsk->comm), 0);
 	}
-	spin_unlock_irqrestore(&running_trace_lock, flags);
+	raw_spin_unlock_irqrestore(&running_trace_lock, flags);
 }
 
 static void trace_note_time(struct blk_trace *bt)
@@ -666,9 +666,9 @@ static int __blk_trace_startstop(struct request_queue *q, int start)
 			blktrace_seq++;
 			smp_mb();
 			bt->trace_state = Blktrace_running;
-			spin_lock_irq(&running_trace_lock);
+			raw_spin_lock_irq(&running_trace_lock);
 			list_add(&bt->running_list, &running_trace_list);
-			spin_unlock_irq(&running_trace_lock);
+			raw_spin_unlock_irq(&running_trace_lock);
 
 			trace_note_time(bt);
 			ret = 0;
@@ -676,9 +676,9 @@ static int __blk_trace_startstop(struct request_queue *q, int start)
 	} else {
 		if (bt->trace_state == Blktrace_running) {
 			bt->trace_state = Blktrace_stopped;
-			spin_lock_irq(&running_trace_lock);
+			raw_spin_lock_irq(&running_trace_lock);
 			list_del_init(&bt->running_list);
-			spin_unlock_irq(&running_trace_lock);
+			raw_spin_unlock_irq(&running_trace_lock);
 			relay_flush(bt->rchan);
 			ret = 0;
 		}
@@ -1608,9 +1608,9 @@ static int blk_trace_remove_queue(struct request_queue *q)
 
 	if (bt->trace_state == Blktrace_running) {
 		bt->trace_state = Blktrace_stopped;
-		spin_lock_irq(&running_trace_lock);
+		raw_spin_lock_irq(&running_trace_lock);
 		list_del_init(&bt->running_list);
-		spin_unlock_irq(&running_trace_lock);
+		raw_spin_unlock_irq(&running_trace_lock);
 		relay_flush(bt->rchan);
 	}
 
-- 
2.27.0

Re: [PATCH v2 1/2] block: Avoid sleeping function called from invalid context bug

[kernel test robot]

Hi Wander,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on axboe-block/for-next]
[also build test ERROR on linux/master linus/master v5.16-rc5]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Wander-Lairson-Costa/Fix-warnings-in-blktrace/20211213-204207
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: x86_64-rhel-8.3-kselftests (https://download.01.org/0day-ci/archive/20211214/202112141554.2175ujH7-lkp@intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/e53f7f8c1ce0b19fef6164247fea08d17d5f771d
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Wander-Lairson-Costa/Fix-warnings-in-blktrace/20211213-204207
        git checkout e53f7f8c1ce0b19fef6164247fea08d17d5f771d
        # save the config file to linux build tree
        mkdir build_dir
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   block/blk-cgroup.c: In function 'blk_cgroup_bio_start':
>> block/blk-cgroup.c:1915:8: error: implicit declaration of function 'get_cpu_light'; did you mean 'em_cpu_get'? [-Werror=implicit-function-declaration]
    1915 |  cpu = get_cpu_light();
         |        ^~~~~~~~~~~~~
         |        em_cpu_get
>> block/blk-cgroup.c:1932:2: error: implicit declaration of function 'put_cpu_light'; did you mean 'fput_light'? [-Werror=implicit-function-declaration]
    1932 |  put_cpu_light();
         |  ^~~~~~~~~~~~~
         |  fput_light
   cc1: some warnings being treated as errors


vim +1915 block/blk-cgroup.c

  1908	
  1909	void blk_cgroup_bio_start(struct bio *bio)
  1910	{
  1911		int rwd = blk_cgroup_io_type(bio), cpu;
  1912		struct blkg_iostat_set *bis;
  1913		unsigned long flags;
  1914	
> 1915		cpu = get_cpu_light();
  1916		bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
  1917		flags = u64_stats_update_begin_irqsave(&bis->sync);
  1918	
  1919		/*
  1920		 * If the bio is flagged with BIO_CGROUP_ACCT it means this is a split
  1921		 * bio and we would have already accounted for the size of the bio.
  1922		 */
  1923		if (!bio_flagged(bio, BIO_CGROUP_ACCT)) {
  1924			bio_set_flag(bio, BIO_CGROUP_ACCT);
  1925			bis->cur.bytes[rwd] += bio->bi_iter.bi_size;
  1926		}
  1927		bis->cur.ios[rwd]++;
  1928	
  1929		u64_stats_update_end_irqrestore(&bis->sync, flags);
  1930		if (cgroup_subsys_on_dfl(io_cgrp_subsys))
  1931			cgroup_rstat_updated(bio->bi_blkg->blkcg->css.cgroup, cpu);
> 1932		put_cpu_light();
  1933	}
  1934	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [PATCH v2 0/2] Fix warnings in blktrace

[Sebastian Andrzej Siewior]

On 2021-12-13 09:37:35 [-0300], Wander Lairson Costa wrote:
> These two patches fix wrong usage of lock primitives with
> CONFIG_PREEMPT_RT in the blktrace code.
> 
> This version fixes a missing piece in the blktrace patch.
> 
> The patches apply to the PREEMPT_RT tree.

I've seen it, need to think about it.

Sebastian

Re: [PATCH v2 1/2] block: Avoid sleeping function called from invalid context bug

[Sebastian Andrzej Siewior]

On 2021-12-13 09:37:36 [-0300], Wander Lairson Costa wrote:
> ---
>  block/blk-cgroup.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 663aabfeba18..0a532bb3003c 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -1911,7 +1911,7 @@ void blk_cgroup_bio_start(struct bio *bio)
>  	struct blkg_iostat_set *bis;
>  	unsigned long flags;
>  
> -	cpu = get_cpu();
> +	cpu = get_cpu_light();
>  	bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
>  	flags = u64_stats_update_begin_irqsave(&bis->sync);
>  
> @@ -1928,7 +1928,7 @@ void blk_cgroup_bio_start(struct bio *bio)
>  	u64_stats_update_end_irqrestore(&bis->sync, flags);
>  	if (cgroup_subsys_on_dfl(io_cgrp_subsys))
>  		cgroup_rstat_updated(bio->bi_blkg->blkcg->css.cgroup, cpu);
> -	put_cpu();
> +	put_cpu_light();
>  }

Are you sure patch and backtrace match? There is also
u64_stats_update_begin_irqsave() which disables preemption on RT. So by
doing what you are suggesting, you only avoid disabling preemption in
cgroup_rstat_updated() which acquires a raw_spinlock_t.

Sebastian

Re: [PATCH v2 2/2] blktrace: switch trace spinlock to a raw spinlock

[Sebastian Andrzej Siewior]

On 2021-12-13 09:37:37 [-0300], Wander Lairson Costa wrote:
…
> To avoid this bug, we switch the trace lock to a raw spinlock.

Steven, do you think this is a good idea?

Sebastian

Re: [PATCH v2 2/2] blktrace: switch trace spinlock to a raw spinlock

[Steven Rostedt]

On Wed, 15 Dec 2021 18:08:34 +0100
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> On 2021-12-13 09:37:37 [-0300], Wander Lairson Costa wrote:
> …
> > To avoid this bug, we switch the trace lock to a raw spinlock.  
> 
> Steven, do you think this is a good idea?
> 

blktrace is actually maintained by Jens.

-- Steve

Re: [PATCH v2 2/2] blktrace: switch trace spinlock to a raw spinlock

[Jens Axboe]

On 12/15/21 10:31 AM, Steven Rostedt wrote:
> On Wed, 15 Dec 2021 18:08:34 +0100
> Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> 
>> On 2021-12-13 09:37:37 [-0300], Wander Lairson Costa wrote:
>> …
>>> To avoid this bug, we switch the trace lock to a raw spinlock.  
>>
>> Steven, do you think this is a good idea?
>>
> 
> blktrace is actually maintained by Jens.

Looks like there are two patches, and none were CC'ed linux-block.
Please resend.

-- 
Jens Axboe

Re: [PATCH v2 1/2] block: Avoid sleeping function called from invalid context bug

[Wander Costa]

On Wed, Dec 15, 2021 at 1:58 PM Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
>
> On 2021-12-13 09:37:36 [-0300], Wander Lairson Costa wrote:
> > ---
> >  block/blk-cgroup.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> > index 663aabfeba18..0a532bb3003c 100644
> > --- a/block/blk-cgroup.c
> > +++ b/block/blk-cgroup.c
> > @@ -1911,7 +1911,7 @@ void blk_cgroup_bio_start(struct bio *bio)
> >       struct blkg_iostat_set *bis;
> >       unsigned long flags;
> >
> > -     cpu = get_cpu();
> > +     cpu = get_cpu_light();
> >       bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
> >       flags = u64_stats_update_begin_irqsave(&bis->sync);
> >
> > @@ -1928,7 +1928,7 @@ void blk_cgroup_bio_start(struct bio *bio)
> >       u64_stats_update_end_irqrestore(&bis->sync, flags);
> >       if (cgroup_subsys_on_dfl(io_cgrp_subsys))
> >               cgroup_rstat_updated(bio->bi_blkg->blkcg->css.cgroup, cpu);
> > -     put_cpu();
> > +     put_cpu_light();
> >  }
>
> Are you sure patch and backtrace match? There is also
> u64_stats_update_begin_irqsave() which disables preemption on RT. So by
> doing what you are suggesting, you only avoid disabling preemption in
> cgroup_rstat_updated() which acquires a raw_spinlock_t.
>

You're right. I double-checked and noticed my tree didn't have the
call to u64_stats_update_begin_irqsave. Only patch 2 is necessary
indeed.

> Sebastian
>

Re: [PATCH v2 2/2] blktrace: switch trace spinlock to a raw spinlock

[Wander Costa]

On Wed, Dec 15, 2021 at 4:34 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 12/15/21 10:31 AM, Steven Rostedt wrote:
> > On Wed, 15 Dec 2021 18:08:34 +0100
> > Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> >
> >> On 2021-12-13 09:37:37 [-0300], Wander Lairson Costa wrote:
> >> …
> >>> To avoid this bug, we switch the trace lock to a raw spinlock.
> >>
> >> Steven, do you think this is a good idea?
> >>
> >
> > blktrace is actually maintained by Jens.
>
> Looks like there are two patches, and none were CC'ed linux-block.
> Please resend.
>
Ok, I am going to do it, thanks.

> --
> Jens Axboe
>