Message-ID: <e52ecabe-7d30-b729-b78c-17984a54d1b4@huawei.com>
Date:   Wed, 2 May 2018 09:47:13 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH v2] f2fs: fix to avoid race during access gc_thread
 pointer

On 2018/4/28 10:36, Jaegeuk Kim wrote:
> On 04/27, Chao Yu wrote:
>> On 2018/4/27 0:03, Jaegeuk Kim wrote:
>>> On 04/24, Chao Yu wrote:
>>>> Thread A			Thread B		Thread C
>>>> - f2fs_remount
>>>>  - stop_gc_thread
>>>> 				- f2fs_sbi_store
>>>> 							- issue_discard_thread
>>>>    sbi->gc_thread = NULL;
>>>> 				  sbi->gc_thread->gc_wake = 1
>>>> 							  access sbi->gc_thread->gc_urgent
>>>>
>>>> Previously, we allocate memory for sbi->gc_thread based on background
>>>> gc thread mount option, the memory can be released if we turn off
>>>> that mount option, but still there are several places access gc_thread
>>>> pointer without considering race condition, result in NULL point
>>>> dereference.
>>>
>>> Do we just need to check &sb->s_umount in f2fs_sbi_store() and
>>
>> Better,
>>
>>> issue_discard_thread?
>>
>> There is more cases can be called from different scenarios:
>> - select_policy()
>> - need_SSR()
> 
> No? They should be blocked by remount(2).

How about below cases?

- do_remount
 - do_remount_sb
  - remount_fs
   - f2fs_remount
    - stop_gc_thread
					- fsync
					 - f2fs_sync_file
					  - file_write_and_wait_range
					   - f2fs_write_data_pages
					    - __write_data_page
					     - should_update_inplace
					      - check_inplace_update_policy
					       - need_SSR
     : sbi->gc_thread = NULL;

or

					     - write_data_page
					      - allocate_data_block
					       - allocate_segment
					        - get_ssr_segment
					         - select_gc_type
     : sbi->gc_thread = NULL;

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>>>
>>>> In order to fix this issue, keep gc_thread structure valid in sbi all
>>>> the time instead of alloc/free it dynamically.
>>>>
>>>> In addition, add a rw semaphore to exclude rw operation in fields of
>>>> gc_thread.
>>>>
>>>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>>>> ---
>>>> v2:
>>>> - add a rw semaphore to exclude rw operation suggested by Jaegeuk.
>>>>  fs/f2fs/debug.c   |  3 +--
>>>>  fs/f2fs/f2fs.h    |  9 ++++++-
>>>>  fs/f2fs/gc.c      | 78 ++++++++++++++++++++++++++++++++++++-------------------
>>>>  fs/f2fs/gc.h      |  1 +
>>>>  fs/f2fs/segment.c | 10 +++++--
>>>>  fs/f2fs/super.c   | 26 +++++++++++++------
>>>>  fs/f2fs/sysfs.c   | 26 ++++++++++++++-----
>>>>  7 files changed, 107 insertions(+), 46 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
>>>> index a66107b5cfff..0fbd674c66fb 100644
>>>> --- a/fs/f2fs/debug.c
>>>> +++ b/fs/f2fs/debug.c
>>>> @@ -221,8 +221,7 @@ static void update_mem_info(struct f2fs_sb_info *sbi)
>>>>  	si->cache_mem = 0;
>>>>  
>>>>  	/* build gc */
>>>> -	if (sbi->gc_thread)
>>>> -		si->cache_mem += sizeof(struct f2fs_gc_kthread);
>>>> +	si->cache_mem += sizeof(struct f2fs_gc_kthread);
>>>>  
>>>>  	/* build merge flush thread */
>>>>  	if (SM_I(sbi)->fcc_info)
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index 8f3ad9662d13..75d3b4875429 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -1412,6 +1412,11 @@ static inline struct sit_info *SIT_I(struct f2fs_sb_info *sbi)
>>>>  	return (struct sit_info *)(SM_I(sbi)->sit_info);
>>>>  }
>>>>  
>>>> +static inline struct f2fs_gc_kthread *GC_I(struct f2fs_sb_info *sbi)
>>>> +{
>>>> +	return (struct f2fs_gc_kthread *)(sbi->gc_thread);
>>>> +}
>>>> +
>>>>  static inline struct free_segmap_info *FREE_I(struct f2fs_sb_info *sbi)
>>>>  {
>>>>  	return (struct free_segmap_info *)(SM_I(sbi)->free_info);
>>>> @@ -2954,8 +2959,10 @@ bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len);
>>>>  /*
>>>>   * gc.c
>>>>   */
>>>> +int init_gc_context(struct f2fs_sb_info *sbi);
>>>> +void destroy_gc_context(struct f2fs_sb_info * sbi);
>>>>  int start_gc_thread(struct f2fs_sb_info *sbi);
>>>> -void stop_gc_thread(struct f2fs_sb_info *sbi);
>>>> +bool stop_gc_thread(struct f2fs_sb_info *sbi);
>>>>  block_t start_bidx_of_node(unsigned int node_ofs, struct inode *inode);
>>>>  int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, bool background,
>>>>  			unsigned int segno);
>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>> index 70418b34c5f6..2febb84b2fd6 100644
>>>> --- a/fs/f2fs/gc.c
>>>> +++ b/fs/f2fs/gc.c
>>>> @@ -26,8 +26,8 @@
>>>>  static int gc_thread_func(void *data)
>>>>  {
>>>>  	struct f2fs_sb_info *sbi = data;
>>>> -	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
>>>> -	wait_queue_head_t *wq = &sbi->gc_thread->gc_wait_queue_head;
>>>> +	struct f2fs_gc_kthread *gc_th = GC_I(sbi);
>>>> +	wait_queue_head_t *wq = &gc_th->gc_wait_queue_head;
>>>>  	unsigned int wait_ms;
>>>>  
>>>>  	wait_ms = gc_th->min_sleep_time;
>>>> @@ -114,17 +114,15 @@ static int gc_thread_func(void *data)
>>>>  	return 0;
>>>>  }
>>>>  
>>>> -int start_gc_thread(struct f2fs_sb_info *sbi)
>>>> +int init_gc_context(struct f2fs_sb_info *sbi)
>>>>  {
>>>>  	struct f2fs_gc_kthread *gc_th;
>>>> -	dev_t dev = sbi->sb->s_bdev->bd_dev;
>>>> -	int err = 0;
>>>>  
>>>>  	gc_th = f2fs_kmalloc(sbi, sizeof(struct f2fs_gc_kthread), GFP_KERNEL);
>>>> -	if (!gc_th) {
>>>> -		err = -ENOMEM;
>>>> -		goto out;
>>>> -	}
>>>> +	if (!gc_th)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	gc_th->f2fs_gc_task = NULL;
>>>>  
>>>>  	gc_th->urgent_sleep_time = DEF_GC_THREAD_URGENT_SLEEP_TIME;
>>>>  	gc_th->min_sleep_time = DEF_GC_THREAD_MIN_SLEEP_TIME;
>>>> @@ -135,35 +133,59 @@ int start_gc_thread(struct f2fs_sb_info *sbi)
>>>>  	gc_th->gc_urgent = 0;
>>>>  	gc_th->gc_wake= 0;
>>>>  
>>>> +	init_rwsem(&gc_th->gc_rwsem);
>>>> +
>>>>  	sbi->gc_thread = gc_th;
>>>> -	init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
>>>> -	sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +void destroy_gc_context(struct f2fs_sb_info *sbi)
>>>> +{
>>>> +	kfree(GC_I(sbi));
>>>> +	sbi->gc_thread = NULL;
>>>> +}
>>>> +
>>>> +int start_gc_thread(struct f2fs_sb_info *sbi)
>>>> +{
>>>> +	struct f2fs_gc_kthread *gc_th = GC_I(sbi);
>>>> +	dev_t dev = sbi->sb->s_bdev->bd_dev;
>>>> +	int err = 0;
>>>> +
>>>> +	init_waitqueue_head(&gc_th->gc_wait_queue_head);
>>>> +	gc_th->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
>>>>  			"f2fs_gc-%u:%u", MAJOR(dev), MINOR(dev));
>>>>  	if (IS_ERR(gc_th->f2fs_gc_task)) {
>>>>  		err = PTR_ERR(gc_th->f2fs_gc_task);
>>>> -		kfree(gc_th);
>>>> -		sbi->gc_thread = NULL;
>>>> +		gc_th->f2fs_gc_task = NULL;
>>>>  	}
>>>> -out:
>>>> +
>>>>  	return err;
>>>>  }
>>>>  
>>>> -void stop_gc_thread(struct f2fs_sb_info *sbi)
>>>> +bool stop_gc_thread(struct f2fs_sb_info *sbi)
>>>>  {
>>>> -	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
>>>> -	if (!gc_th)
>>>> -		return;
>>>> -	kthread_stop(gc_th->f2fs_gc_task);
>>>> -	kfree(gc_th);
>>>> -	sbi->gc_thread = NULL;
>>>> +	struct f2fs_gc_kthread *gc_th = GC_I(sbi);
>>>> +	bool stopped = false;
>>>> +
>>>> +	down_write(&gc_th->gc_rwsem);
>>>> +	if (gc_th->f2fs_gc_task) {
>>>> +		kthread_stop(gc_th->f2fs_gc_task);
>>>> +		gc_th->f2fs_gc_task = NULL;
>>>> +		stopped = true;
>>>> +	}
>>>> +	up_write(&gc_th->gc_rwsem);
>>>> +
>>>> +	return stopped;
>>>>  }
>>>>  
>>>>  static int select_gc_type(struct f2fs_gc_kthread *gc_th, int gc_type)
>>>>  {
>>>>  	int gc_mode = (gc_type == BG_GC) ? GC_CB : GC_GREEDY;
>>>>  
>>>> -	if (!gc_th)
>>>> -		return gc_mode;
>>>> +	down_read(&gc_th->gc_rwsem);
>>>> +	if (!gc_th->f2fs_gc_task)
>>>> +		goto out;
>>>>  
>>>>  	if (gc_th->gc_idle) {
>>>>  		if (gc_th->gc_idle == 1)
>>>> @@ -173,6 +195,8 @@ static int select_gc_type(struct f2fs_gc_kthread *gc_th, int gc_type)
>>>>  	}
>>>>  	if (gc_th->gc_urgent)
>>>>  		gc_mode = GC_GREEDY;
>>>> +out:
>>>> +	up_read(&gc_th->gc_rwsem);
>>>>  	return gc_mode;
>>>>  }
>>>>  
>>>> @@ -187,17 +211,19 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
>>>>  		p->max_search = dirty_i->nr_dirty[type];
>>>>  		p->ofs_unit = 1;
>>>>  	} else {
>>>> -		p->gc_mode = select_gc_type(sbi->gc_thread, gc_type);
>>>> +		p->gc_mode = select_gc_type(GC_I(sbi), gc_type);
>>>>  		p->dirty_segmap = dirty_i->dirty_segmap[DIRTY];
>>>>  		p->max_search = dirty_i->nr_dirty[DIRTY];
>>>>  		p->ofs_unit = sbi->segs_per_sec;
>>>>  	}
>>>>  
>>>>  	/* we need to check every dirty segments in the FG_GC case */
>>>> -	if (gc_type != FG_GC &&
>>>> -			(sbi->gc_thread && !sbi->gc_thread->gc_urgent) &&
>>>> +	down_read(&GC_I(sbi)->gc_rwsem);
>>>> +	if (gc_type != FG_GC && GC_I(sbi)->f2fs_gc_task &&
>>>> +			!GC_I(sbi)->gc_urgent &&
>>>>  			p->max_search > sbi->max_victim_search)
>>>>  		p->max_search = sbi->max_victim_search;
>>>> +	up_read(&GC_I(sbi)->gc_rwsem);
>>>>  
>>>>  	/* let's select beginning hot/small space first in no_heap mode*/
>>>>  	if (test_opt(sbi, NOHEAP) &&
>>>> diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
>>>> index b0045d4c8d1e..9a5b273328c2 100644
>>>> --- a/fs/f2fs/gc.h
>>>> +++ b/fs/f2fs/gc.h
>>>> @@ -26,6 +26,7 @@
>>>>  #define DEF_MAX_VICTIM_SEARCH 4096 /* covers 8GB */
>>>>  
>>>>  struct f2fs_gc_kthread {
>>>> +	struct rw_semaphore gc_rwsem;		/* semaphore for f2fs_gc_task */
>>>>  	struct task_struct *f2fs_gc_task;
>>>>  	wait_queue_head_t gc_wait_queue_head;
>>>>  
>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>> index 5960768d26df..f787eea1b2f6 100644
>>>> --- a/fs/f2fs/segment.c
>>>> +++ b/fs/f2fs/segment.c
>>>> @@ -177,8 +177,12 @@ bool need_SSR(struct f2fs_sb_info *sbi)
>>>>  
>>>>  	if (test_opt(sbi, LFS))
>>>>  		return false;
>>>> -	if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
>>>> +	down_read(&GC_I(sbi)->gc_rwsem);
>>>> +	if (GC_I(sbi)->f2fs_gc_task && GC_I(sbi)->gc_urgent) {
>>>> +		down_read(&GC_I(sbi)->gc_rwsem);
>>>>  		return true;
>>>> +	}
>>>> +	up_read(&GC_I(sbi)->gc_rwsem);
>>>>  
>>>>  	return free_sections(sbi) <= (node_secs + 2 * dent_secs + imeta_secs +
>>>>  			SM_I(sbi)->min_ssr_sections + reserved_sections(sbi));
>>>> @@ -1425,8 +1429,10 @@ static int issue_discard_thread(void *data)
>>>>  		if (dcc->discard_wake)
>>>>  			dcc->discard_wake = 0;
>>>>  
>>>> -		if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
>>>> +		down_read(&GC_I(sbi)->gc_rwsem);
>>>> +		if (GC_I(sbi)->f2fs_gc_task && GC_I(sbi)->gc_urgent)
>>>>  			init_discard_policy(&dpolicy, DPOLICY_FORCE, 1);
>>>> +		up_read(&GC_I(sbi)->gc_rwsem);
>>>>  
>>>>  		sb_start_intwrite(sbi->sb);
>>>>  
>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>> index dedb8e50b440..199f29dce86d 100644
>>>> --- a/fs/f2fs/super.c
>>>> +++ b/fs/f2fs/super.c
>>>> @@ -1044,6 +1044,7 @@ static void f2fs_put_super(struct super_block *sb)
>>>>  	kfree(sbi->raw_super);
>>>>  
>>>>  	destroy_device_list(sbi);
>>>> +	destroy_gc_context(sbi);
>>>>  	mempool_destroy(sbi->write_io_dummy);
>>>>  #ifdef CONFIG_QUOTA
>>>>  	for (i = 0; i < MAXQUOTAS; i++)
>>>> @@ -1476,15 +1477,18 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
>>>>  	 * option. Also sync the filesystem.
>>>>  	 */
>>>>  	if ((*flags & SB_RDONLY) || !test_opt(sbi, BG_GC)) {
>>>> -		if (sbi->gc_thread) {
>>>> -			stop_gc_thread(sbi);
>>>> -			need_restart_gc = true;
>>>> +		need_restart_gc = stop_gc_thread(sbi);
>>>> +	} else {
>>>> +		down_write(&GC_I(sbi)->gc_rwsem);
>>>> +		if (!GC_I(sbi)->f2fs_gc_task) {
>>>> +			err = start_gc_thread(sbi);
>>>> +			if (err) {
>>>> +				up_write(&GC_I(sbi)->gc_rwsem);
>>>> +				goto restore_opts;
>>>> +			}
>>>> +			need_stop_gc = true;
>>>>  		}
>>>> -	} else if (!sbi->gc_thread) {
>>>> -		err = start_gc_thread(sbi);
>>>> -		if (err)
>>>> -			goto restore_opts;
>>>> -		need_stop_gc = true;
>>>> +		up_write(&GC_I(sbi)->gc_rwsem);
>>>>  	}
>>>>  
>>>>  	if (*flags & SB_RDONLY ||
>>>> @@ -2771,6 +2775,10 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>>>>  		goto free_meta_inode;
>>>>  	}
>>>>  
>>>> +	err = init_gc_context(sbi);
>>>> +	if (err)
>>>> +		goto free_checkpoint;
>>>> +
>>>>  	/* Initialize device list */
>>>>  	err = f2fs_scan_devices(sbi);
>>>>  	if (err) {
>>>> @@ -2981,6 +2989,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>>>>  	destroy_segment_manager(sbi);
>>>>  free_devices:
>>>>  	destroy_device_list(sbi);
>>>> +	destroy_gc_context(sbi);
>>>> +free_checkpoint:
>>>>  	kfree(sbi->ckpt);
>>>>  free_meta_inode:
>>>>  	make_bad_inode(sbi->meta_inode);
>>>> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
>>>> index 2c53de9251be..b8d09935e43f 100644
>>>> --- a/fs/f2fs/sysfs.c
>>>> +++ b/fs/f2fs/sysfs.c
>>>> @@ -46,7 +46,7 @@ struct f2fs_attr {
>>>>  static unsigned char *__struct_ptr(struct f2fs_sb_info *sbi, int struct_type)
>>>>  {
>>>>  	if (struct_type == GC_THREAD)
>>>> -		return (unsigned char *)sbi->gc_thread;
>>>> +		return (unsigned char *)GC_I(sbi);
>>>>  	else if (struct_type == SM_INFO)
>>>>  		return (unsigned char *)SM_I(sbi);
>>>>  	else if (struct_type == DCC_INFO)
>>>> @@ -248,16 +248,28 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
>>>>  	if (!strcmp(a->attr.name, "trim_sections"))
>>>>  		return -EINVAL;
>>>>  
>>>> -	*ui = t;
>>>> -
>>>> -	if (!strcmp(a->attr.name, "iostat_enable") && *ui == 0)
>>>> +	if (!strcmp(a->attr.name, "iostat_enable") && t == 0)
>>>>  		f2fs_reset_iostat(sbi);
>>>> -	if (!strcmp(a->attr.name, "gc_urgent") && t == 1 && sbi->gc_thread) {
>>>> -		sbi->gc_thread->gc_wake = 1;
>>>> -		wake_up_interruptible_all(&sbi->gc_thread->gc_wait_queue_head);
>>>> +
>>>> +	if (a->struct_type == GC_THREAD) {
>>>> +		down_write(&GC_I(sbi)->gc_rwsem);
>>>> +		if (!GC_I(sbi)->f2fs_gc_task) {
>>>> +			up_write(&GC_I(sbi)->gc_rwsem);
>>>> +			return -EINVAL;
>>>> +		}
>>>> +	}
>>>> +
>>>> +	if (!strcmp(a->attr.name, "gc_urgent") && t == 1) {
>>>> +		GC_I(sbi)->gc_wake = 1;
>>>> +		wake_up_interruptible_all(&GC_I(sbi)->gc_wait_queue_head);
>>>>  		wake_up_discard_thread(sbi, true);
>>>>  	}
>>>>  
>>>> +	*ui = t;
>>>> +
>>>> +	if (a->struct_type == GC_THREAD)
>>>> +		up_write(&GC_I(sbi)->gc_rwsem);
>>>> +
>>>>  	return count;
>>>>  }
>>>>  
>>>> -- 
>>>> 2.15.0.55.gc2ece9dc4de6
>>>
>>> .
>>>
> 
> .
> 

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