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* [f2fs-dev] [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc()
@ 2019-08-06 11:19 Sahitya Tummala
  2019-08-07  2:04 ` Chao Yu
  0 siblings, 1 reply; 5+ messages in thread
From: Sahitya Tummala @ 2019-08-06 11:19 UTC (permalink / raw)
  To: Jaegeuk Kim, Chao Yu, linux-f2fs-devel; +Cc: linux-kernel

Policy - Foreground GC, LFS and greedy GC mode.

Under this policy, f2fs_gc() loops forever to GC as it doesn't have
enough free segements to proceed and thus it keeps calling gc_more
for the same victim segment.  This can happen if the selected victim
segment could not be GC'd due to failed blkaddr validity check i.e.
is_alive() returns false for the blocks set in current validity map.

Fix this by keeping track of such invalid segments and skip those
segments for selection in get_victim_by_default() to avoid endless
GC loop under such error scenarios.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
---
v2: fix as per Chao's suggestion to handle this error case

 fs/f2fs/gc.c      | 15 ++++++++++++++-
 fs/f2fs/segment.c |  5 +++++
 fs/f2fs/segment.h |  3 +++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 8974672..321a78a 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -382,6 +382,14 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
 			nsearched++;
 		}
 
+		/*
+		 * skip selecting the invalid segno (that is failed due to block
+		 * validity check failed during GC) to avoid endless GC loop in
+		 * such cases.
+		 */
+		if (test_bit(segno, sm->invalid_segmap))
+			goto next;
+
 		secno = GET_SEC_FROM_SEG(sbi, segno);
 
 		if (sec_usage_check(sbi, secno))
@@ -975,6 +983,7 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 	int off;
 	int phase = 0;
 	int submitted = 0;
+	struct sit_info *sit_i = SIT_I(sbi);
 
 	start_addr = START_BLOCK(sbi, segno);
 
@@ -1008,8 +1017,12 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 		}
 
 		/* Get an inode by ino with checking validity */
-		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs))
+		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs)) {
+			if (!test_and_set_bit(segno, sit_i->invalid_segmap))
+				f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
+						start_addr + off, segno);
 			continue;
+		}
 
 		if (phase == 2) {
 			f2fs_ra_node_page(sbi, dni.ino);
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index a661ac3..d45a1d3 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -4017,6 +4017,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
 		return -ENOMEM;
 #endif
 
+	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
+	if (!sit_i->invalid_segmap)
+		return -ENOMEM;
+
 	/* init SIT information */
 	sit_i->s_ops = &default_salloc_ops;
 
@@ -4518,6 +4522,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
 #ifdef CONFIG_F2FS_CHECK_FS
 	kvfree(sit_i->sit_bitmap_mir);
 #endif
+	kvfree(sit_i->invalid_segmap);
 	kvfree(sit_i);
 }
 
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index b746028..bc5dbe8 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -246,6 +246,9 @@ struct sit_info {
 	unsigned long long min_mtime;		/* min. modification time */
 	unsigned long long max_mtime;		/* max. modification time */
 
+	/* list of segments to be ignored by GC in case of errors */
+	unsigned long *invalid_segmap;
+
 	unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
 };
 
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.



_______________________________________________
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Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [f2fs-dev] [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc()
  2019-08-06 11:19 [f2fs-dev] [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc() Sahitya Tummala
@ 2019-08-07  2:04 ` Chao Yu
  2019-08-07  3:24   ` Sahitya Tummala
  0 siblings, 1 reply; 5+ messages in thread
From: Chao Yu @ 2019-08-07  2:04 UTC (permalink / raw)
  To: Sahitya Tummala, Jaegeuk Kim, linux-f2fs-devel; +Cc: linux-kernel

Hi Sahitya,

On 2019/8/6 19:19, Sahitya Tummala wrote:
> Policy - Foreground GC, LFS and greedy GC mode.
> 
> Under this policy, f2fs_gc() loops forever to GC as it doesn't have
> enough free segements to proceed and thus it keeps calling gc_more
> for the same victim segment.  This can happen if the selected victim
> segment could not be GC'd due to failed blkaddr validity check i.e.
> is_alive() returns false for the blocks set in current validity map.
> 
> Fix this by keeping track of such invalid segments and skip those
> segments for selection in get_victim_by_default() to avoid endless
> GC loop under such error scenarios.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> ---
> v2: fix as per Chao's suggestion to handle this error case
> 
>  fs/f2fs/gc.c      | 15 ++++++++++++++-
>  fs/f2fs/segment.c |  5 +++++
>  fs/f2fs/segment.h |  3 +++
>  3 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 8974672..321a78a 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -382,6 +382,14 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
>  			nsearched++;
>  		}
>  
> +		/*
> +		 * skip selecting the invalid segno (that is failed due to block
> +		 * validity check failed during GC) to avoid endless GC loop in
> +		 * such cases.
> +		 */
> +		if (test_bit(segno, sm->invalid_segmap))
> +			goto next;
> +
>  		secno = GET_SEC_FROM_SEG(sbi, segno);
>  
>  		if (sec_usage_check(sbi, secno))
> @@ -975,6 +983,7 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>  	int off;
>  	int phase = 0;
>  	int submitted = 0;
> +	struct sit_info *sit_i = SIT_I(sbi);
>  
>  	start_addr = START_BLOCK(sbi, segno);
>  
> @@ -1008,8 +1017,12 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>  		}
>  
>  		/* Get an inode by ino with checking validity */
> -		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs))
> +		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs)) {
> +			if (!test_and_set_bit(segno, sit_i->invalid_segmap))
> +				f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
> +						start_addr + off, segno);

Oh, there is some normal cases in is_alive(), such as f2fs_get_node_page() or
f2fs_get_node_info() failure due to no memory, we should bypass such cases. I
guess something like this:

if (source_blkaddr != blkaddr) {
	if (unlikely(check_valid_map(sbi, segno, off))) {
		if (!test_and_set_bit(segno, sit_i->invalid_segmap)) {
			f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
				start_addr + off, segno);
			set_sbi_flag(sbi, SBI_NEED_FSCK);
		}
	}
	return false;
}

I think this will be safe to call check_valid_map(), because there should be no
race in between is_alive() and update_sit_entry() from all paths due to node
page lock dependence.

One more concern is should we use this under CONFIG_F2FS_CHECK_FS? If there is
actually such a bug can cause data inconsistency, we'd better find the root
cause in debug version.

Thanks,

>  			continue;
> +		}
>  
>  		if (phase == 2) {
>  			f2fs_ra_node_page(sbi, dni.ino);
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index a661ac3..d45a1d3 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -4017,6 +4017,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
>  		return -ENOMEM;
>  #endif
>  
> +	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
> +	if (!sit_i->invalid_segmap)
> +		return -ENOMEM;
> +
>  	/* init SIT information */
>  	sit_i->s_ops = &default_salloc_ops;
>  
> @@ -4518,6 +4522,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
>  #ifdef CONFIG_F2FS_CHECK_FS
>  	kvfree(sit_i->sit_bitmap_mir);
>  #endif
> +	kvfree(sit_i->invalid_segmap);
>  	kvfree(sit_i);
>  }
>  
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index b746028..bc5dbe8 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -246,6 +246,9 @@ struct sit_info {
>  	unsigned long long min_mtime;		/* min. modification time */
>  	unsigned long long max_mtime;		/* max. modification time */
>  
> +	/* list of segments to be ignored by GC in case of errors */
> +	unsigned long *invalid_segmap;
> +
>  	unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
>  };
>  
> 


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^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [f2fs-dev] [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc()
  2019-08-07  2:04 ` Chao Yu
@ 2019-08-07  3:24   ` Sahitya Tummala
  2019-08-07  3:37     ` Chao Yu
  0 siblings, 1 reply; 5+ messages in thread
From: Sahitya Tummala @ 2019-08-07  3:24 UTC (permalink / raw)
  To: Chao Yu; +Cc: Jaegeuk Kim, linux-kernel, linux-f2fs-devel

Hi Chao,

On Wed, Aug 07, 2019 at 10:04:16AM +0800, Chao Yu wrote:
> Hi Sahitya,
> 
> On 2019/8/6 19:19, Sahitya Tummala wrote:
> > Policy - Foreground GC, LFS and greedy GC mode.
> > 
> > Under this policy, f2fs_gc() loops forever to GC as it doesn't have
> > enough free segements to proceed and thus it keeps calling gc_more
> > for the same victim segment.  This can happen if the selected victim
> > segment could not be GC'd due to failed blkaddr validity check i.e.
> > is_alive() returns false for the blocks set in current validity map.
> > 
> > Fix this by keeping track of such invalid segments and skip those
> > segments for selection in get_victim_by_default() to avoid endless
> > GC loop under such error scenarios.
> > 
> > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > ---
> > v2: fix as per Chao's suggestion to handle this error case
> > 
> >  fs/f2fs/gc.c      | 15 ++++++++++++++-
> >  fs/f2fs/segment.c |  5 +++++
> >  fs/f2fs/segment.h |  3 +++
> >  3 files changed, 22 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index 8974672..321a78a 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -382,6 +382,14 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
> >  			nsearched++;
> >  		}
> >  
> > +		/*
> > +		 * skip selecting the invalid segno (that is failed due to block
> > +		 * validity check failed during GC) to avoid endless GC loop in
> > +		 * such cases.
> > +		 */
> > +		if (test_bit(segno, sm->invalid_segmap))
> > +			goto next;
> > +
> >  		secno = GET_SEC_FROM_SEG(sbi, segno);
> >  
> >  		if (sec_usage_check(sbi, secno))
> > @@ -975,6 +983,7 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >  	int off;
> >  	int phase = 0;
> >  	int submitted = 0;
> > +	struct sit_info *sit_i = SIT_I(sbi);
> >  
> >  	start_addr = START_BLOCK(sbi, segno);
> >  
> > @@ -1008,8 +1017,12 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >  		}
> >  
> >  		/* Get an inode by ino with checking validity */
> > -		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs))
> > +		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs)) {
> > +			if (!test_and_set_bit(segno, sit_i->invalid_segmap))
> > +				f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
> > +						start_addr + off, segno);
> 
> Oh, there is some normal cases in is_alive(), such as f2fs_get_node_page() or
> f2fs_get_node_info() failure due to no memory, we should bypass such cases. I

Oh, yes, I have missed this point.

> guess something like this:
> 
> if (source_blkaddr != blkaddr) {
> 	if (unlikely(check_valid_map(sbi, segno, off))) {

check_valid_map() is validated before is_alive(). So I think this check again
may not be needed. What do you think?

> 		if (!test_and_set_bit(segno, sit_i->invalid_segmap)) {
> 			f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
> 				start_addr + off, segno);
> 			set_sbi_flag(sbi, SBI_NEED_FSCK);
> 		}
> 	}
> 	return false;
> }
> 
> I think this will be safe to call check_valid_map(), because there should be no
> race in between is_alive() and update_sit_entry() from all paths due to node
> page lock dependence.
> 
> One more concern is should we use this under CONFIG_F2FS_CHECK_FS? If there is
> actually such a bug can cause data inconsistency, we'd better find the root
> cause in debug version.
> 

Yes, I agree with you. I will include this under CONFIG_F2FS_CHECK_FS.

Thanks,

> Thanks,
> 
> >  			continue;
> > +		}
> >  
> >  		if (phase == 2) {
> >  			f2fs_ra_node_page(sbi, dni.ino);
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index a661ac3..d45a1d3 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -4017,6 +4017,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
> >  		return -ENOMEM;
> >  #endif
> >  
> > +	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
> > +	if (!sit_i->invalid_segmap)
> > +		return -ENOMEM;
> > +
> >  	/* init SIT information */
> >  	sit_i->s_ops = &default_salloc_ops;
> >  
> > @@ -4518,6 +4522,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
> >  #ifdef CONFIG_F2FS_CHECK_FS
> >  	kvfree(sit_i->sit_bitmap_mir);
> >  #endif
> > +	kvfree(sit_i->invalid_segmap);
> >  	kvfree(sit_i);
> >  }
> >  
> > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > index b746028..bc5dbe8 100644
> > --- a/fs/f2fs/segment.h
> > +++ b/fs/f2fs/segment.h
> > @@ -246,6 +246,9 @@ struct sit_info {
> >  	unsigned long long min_mtime;		/* min. modification time */
> >  	unsigned long long max_mtime;		/* max. modification time */
> >  
> > +	/* list of segments to be ignored by GC in case of errors */
> > +	unsigned long *invalid_segmap;
> > +
> >  	unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
> >  };
> >  
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [f2fs-dev] [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc()
  2019-08-07  3:24   ` Sahitya Tummala
@ 2019-08-07  3:37     ` Chao Yu
  2019-08-07  5:14       ` Sahitya Tummala
  0 siblings, 1 reply; 5+ messages in thread
From: Chao Yu @ 2019-08-07  3:37 UTC (permalink / raw)
  To: Sahitya Tummala; +Cc: Jaegeuk Kim, linux-kernel, linux-f2fs-devel

Hi Sahitya,

On 2019/8/7 11:24, Sahitya Tummala wrote:
> Hi Chao,
> 
> On Wed, Aug 07, 2019 at 10:04:16AM +0800, Chao Yu wrote:
>> Hi Sahitya,
>>
>> On 2019/8/6 19:19, Sahitya Tummala wrote:
>>> Policy - Foreground GC, LFS and greedy GC mode.
>>>
>>> Under this policy, f2fs_gc() loops forever to GC as it doesn't have
>>> enough free segements to proceed and thus it keeps calling gc_more
>>> for the same victim segment.  This can happen if the selected victim
>>> segment could not be GC'd due to failed blkaddr validity check i.e.
>>> is_alive() returns false for the blocks set in current validity map.
>>>
>>> Fix this by keeping track of such invalid segments and skip those
>>> segments for selection in get_victim_by_default() to avoid endless
>>> GC loop under such error scenarios.
>>>
>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>> ---
>>> v2: fix as per Chao's suggestion to handle this error case
>>>
>>>  fs/f2fs/gc.c      | 15 ++++++++++++++-
>>>  fs/f2fs/segment.c |  5 +++++
>>>  fs/f2fs/segment.h |  3 +++
>>>  3 files changed, 22 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>> index 8974672..321a78a 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -382,6 +382,14 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
>>>  			nsearched++;
>>>  		}
>>>  
>>> +		/*
>>> +		 * skip selecting the invalid segno (that is failed due to block
>>> +		 * validity check failed during GC) to avoid endless GC loop in
>>> +		 * such cases.
>>> +		 */
>>> +		if (test_bit(segno, sm->invalid_segmap))
>>> +			goto next;
>>> +
>>>  		secno = GET_SEC_FROM_SEG(sbi, segno);
>>>  
>>>  		if (sec_usage_check(sbi, secno))
>>> @@ -975,6 +983,7 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>>>  	int off;
>>>  	int phase = 0;
>>>  	int submitted = 0;
>>> +	struct sit_info *sit_i = SIT_I(sbi);
>>>  
>>>  	start_addr = START_BLOCK(sbi, segno);
>>>  
>>> @@ -1008,8 +1017,12 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>>>  		}
>>>  
>>>  		/* Get an inode by ino with checking validity */
>>> -		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs))
>>> +		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs)) {
>>> +			if (!test_and_set_bit(segno, sit_i->invalid_segmap))
>>> +				f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
>>> +						start_addr + off, segno);
>>
>> Oh, there is some normal cases in is_alive(), such as f2fs_get_node_page() or
>> f2fs_get_node_info() failure due to no memory, we should bypass such cases. I
> 
> Oh, yes, I have missed this point.
> 
>> guess something like this:
>>
>> if (source_blkaddr != blkaddr) {
>> 	if (unlikely(check_valid_map(sbi, segno, off))) {
> 
> check_valid_map() is validated before is_alive(). So I think this check again
> may not be needed. What do you think?

> race in between is_alive() and update_sit_entry()

There will be a race case:

gc_data_segment			f2fs_truncate_data_blocks_range
check_valid_map
				f2fs_invalidate_blocks
				update_sit_entry
				f2fs_test_and_clear_bit(, se->cur_valid_map);
				unlock_page(node_page)
is_alive
lock_page(node_page)
blkaddr should be NULL and not equal to source_blkaddr, I think this is a normal
case, right?

Thanks,

> 
>> 		if (!test_and_set_bit(segno, sit_i->invalid_segmap)) {
>> 			f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
>> 				start_addr + off, segno);
>> 			set_sbi_flag(sbi, SBI_NEED_FSCK);
>> 		}
>> 	}
>> 	return false;
>> }
>>
>> I think this will be safe to call check_valid_map(), because there should be no
>> race in between is_alive() and update_sit_entry() from all paths due to node
>> page lock dependence.
>>
>> One more concern is should we use this under CONFIG_F2FS_CHECK_FS? If there is
>> actually such a bug can cause data inconsistency, we'd better find the root
>> cause in debug version.
>>
> 
> Yes, I agree with you. I will include this under CONFIG_F2FS_CHECK_FS.
> 
> Thanks,
> 
>> Thanks,
>>
>>>  			continue;
>>> +		}
>>>  
>>>  		if (phase == 2) {
>>>  			f2fs_ra_node_page(sbi, dni.ino);
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index a661ac3..d45a1d3 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -4017,6 +4017,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
>>>  		return -ENOMEM;
>>>  #endif
>>>  
>>> +	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
>>> +	if (!sit_i->invalid_segmap)
>>> +		return -ENOMEM;
>>> +
>>>  	/* init SIT information */
>>>  	sit_i->s_ops = &default_salloc_ops;
>>>  
>>> @@ -4518,6 +4522,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
>>>  #ifdef CONFIG_F2FS_CHECK_FS
>>>  	kvfree(sit_i->sit_bitmap_mir);
>>>  #endif
>>> +	kvfree(sit_i->invalid_segmap);
>>>  	kvfree(sit_i);
>>>  }
>>>  
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index b746028..bc5dbe8 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -246,6 +246,9 @@ struct sit_info {
>>>  	unsigned long long min_mtime;		/* min. modification time */
>>>  	unsigned long long max_mtime;		/* max. modification time */
>>>  
>>> +	/* list of segments to be ignored by GC in case of errors */
>>> +	unsigned long *invalid_segmap;
>>> +
>>>  	unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
>>>  };
>>>  
>>>
> 


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* Re: [f2fs-dev] [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc()
  2019-08-07  3:37     ` Chao Yu
@ 2019-08-07  5:14       ` Sahitya Tummala
  0 siblings, 0 replies; 5+ messages in thread
From: Sahitya Tummala @ 2019-08-07  5:14 UTC (permalink / raw)
  To: Chao Yu; +Cc: Jaegeuk Kim, linux-kernel, linux-f2fs-devel

On Wed, Aug 07, 2019 at 11:37:22AM +0800, Chao Yu wrote:
> Hi Sahitya,
> 
> On 2019/8/7 11:24, Sahitya Tummala wrote:
> > Hi Chao,
> > 
> > On Wed, Aug 07, 2019 at 10:04:16AM +0800, Chao Yu wrote:
> >> Hi Sahitya,
> >>
> >> On 2019/8/6 19:19, Sahitya Tummala wrote:
> >>> Policy - Foreground GC, LFS and greedy GC mode.
> >>>
> >>> Under this policy, f2fs_gc() loops forever to GC as it doesn't have
> >>> enough free segements to proceed and thus it keeps calling gc_more
> >>> for the same victim segment.  This can happen if the selected victim
> >>> segment could not be GC'd due to failed blkaddr validity check i.e.
> >>> is_alive() returns false for the blocks set in current validity map.
> >>>
> >>> Fix this by keeping track of such invalid segments and skip those
> >>> segments for selection in get_victim_by_default() to avoid endless
> >>> GC loop under such error scenarios.
> >>>
> >>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> >>> ---
> >>> v2: fix as per Chao's suggestion to handle this error case
> >>>
> >>>  fs/f2fs/gc.c      | 15 ++++++++++++++-
> >>>  fs/f2fs/segment.c |  5 +++++
> >>>  fs/f2fs/segment.h |  3 +++
> >>>  3 files changed, 22 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >>> index 8974672..321a78a 100644
> >>> --- a/fs/f2fs/gc.c
> >>> +++ b/fs/f2fs/gc.c
> >>> @@ -382,6 +382,14 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
> >>>  			nsearched++;
> >>>  		}
> >>>  
> >>> +		/*
> >>> +		 * skip selecting the invalid segno (that is failed due to block
> >>> +		 * validity check failed during GC) to avoid endless GC loop in
> >>> +		 * such cases.
> >>> +		 */
> >>> +		if (test_bit(segno, sm->invalid_segmap))
> >>> +			goto next;
> >>> +
> >>>  		secno = GET_SEC_FROM_SEG(sbi, segno);
> >>>  
> >>>  		if (sec_usage_check(sbi, secno))
> >>> @@ -975,6 +983,7 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >>>  	int off;
> >>>  	int phase = 0;
> >>>  	int submitted = 0;
> >>> +	struct sit_info *sit_i = SIT_I(sbi);
> >>>  
> >>>  	start_addr = START_BLOCK(sbi, segno);
> >>>  
> >>> @@ -1008,8 +1017,12 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >>>  		}
> >>>  
> >>>  		/* Get an inode by ino with checking validity */
> >>> -		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs))
> >>> +		if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs)) {
> >>> +			if (!test_and_set_bit(segno, sit_i->invalid_segmap))
> >>> +				f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
> >>> +						start_addr + off, segno);
> >>
> >> Oh, there is some normal cases in is_alive(), such as f2fs_get_node_page() or
> >> f2fs_get_node_info() failure due to no memory, we should bypass such cases. I
> > 
> > Oh, yes, I have missed this point.
> > 
> >> guess something like this:
> >>
> >> if (source_blkaddr != blkaddr) {
> >> 	if (unlikely(check_valid_map(sbi, segno, off))) {
> > 
> > check_valid_map() is validated before is_alive(). So I think this check again
> > may not be needed. What do you think?
> 
> > race in between is_alive() and update_sit_entry()
> 
> There will be a race case:
> 
> gc_data_segment			f2fs_truncate_data_blocks_range
> check_valid_map
> 				f2fs_invalidate_blocks
> 				update_sit_entry
> 				f2fs_test_and_clear_bit(, se->cur_valid_map);
> 				unlock_page(node_page)
> is_alive
> lock_page(node_page)
> blkaddr should be NULL and not equal to source_blkaddr, I think this is a normal
> case, right?
> 

Got it, thanks for the clarification.

> Thanks,
> 
> > 
> >> 		if (!test_and_set_bit(segno, sit_i->invalid_segmap)) {
> >> 			f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
> >> 				start_addr + off, segno);
> >> 			set_sbi_flag(sbi, SBI_NEED_FSCK);
> >> 		}
> >> 	}
> >> 	return false;
> >> }
> >>
> >> I think this will be safe to call check_valid_map(), because there should be no
> >> race in between is_alive() and update_sit_entry() from all paths due to node
> >> page lock dependence.
> >>
> >> One more concern is should we use this under CONFIG_F2FS_CHECK_FS? If there is
> >> actually such a bug can cause data inconsistency, we'd better find the root
> >> cause in debug version.
> >>
> > 
> > Yes, I agree with you. I will include this under CONFIG_F2FS_CHECK_FS.
> > 
> > Thanks,
> > 
> >> Thanks,
> >>
> >>>  			continue;
> >>> +		}
> >>>  
> >>>  		if (phase == 2) {
> >>>  			f2fs_ra_node_page(sbi, dni.ino);
> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>> index a661ac3..d45a1d3 100644
> >>> --- a/fs/f2fs/segment.c
> >>> +++ b/fs/f2fs/segment.c
> >>> @@ -4017,6 +4017,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
> >>>  		return -ENOMEM;
> >>>  #endif
> >>>  
> >>> +	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
> >>> +	if (!sit_i->invalid_segmap)
> >>> +		return -ENOMEM;
> >>> +
> >>>  	/* init SIT information */
> >>>  	sit_i->s_ops = &default_salloc_ops;
> >>>  
> >>> @@ -4518,6 +4522,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
> >>>  #ifdef CONFIG_F2FS_CHECK_FS
> >>>  	kvfree(sit_i->sit_bitmap_mir);
> >>>  #endif
> >>> +	kvfree(sit_i->invalid_segmap);
> >>>  	kvfree(sit_i);
> >>>  }
> >>>  
> >>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> >>> index b746028..bc5dbe8 100644
> >>> --- a/fs/f2fs/segment.h
> >>> +++ b/fs/f2fs/segment.h
> >>> @@ -246,6 +246,9 @@ struct sit_info {
> >>>  	unsigned long long min_mtime;		/* min. modification time */
> >>>  	unsigned long long max_mtime;		/* max. modification time */
> >>>  
> >>> +	/* list of segments to be ignored by GC in case of errors */
> >>> +	unsigned long *invalid_segmap;
> >>> +
> >>>  	unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
> >>>  };
> >>>  
> >>>
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


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^ permalink raw reply	[flat|nested] 5+ messages in thread

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Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-08-06 11:19 [f2fs-dev] [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc() Sahitya Tummala
2019-08-07  2:04 ` Chao Yu
2019-08-07  3:24   ` Sahitya Tummala
2019-08-07  3:37     ` Chao Yu
2019-08-07  5:14       ` Sahitya Tummala

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