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Date:   Tue, 17 Sep 2019 11:03:16 +0530
From:   Sahitya Tummala <stummala@codeaurora.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-f2fs-devel@lists.sourceforge.net, Chao Yu <chao@kernel.org>,
        Jaegeuk Kim <jaegeuk@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [f2fs-dev] [PATCH v4] f2fs: Fix indefinite loop in f2fs_gc()
Message-ID: <20190917053316.GB12730@codeaurora.org>
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 <355d24c1-b07c-f8ff-1ab9-3f85653ced60@huawei.com>
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Hi Chao,

On Fri, Sep 06, 2019 at 07:00:32PM +0800, Chao Yu wrote:
> Hi Sahitya,
> 
> Luckily, I can reproduce this issue with generic/269, and have sent another
> patch for the issue, could you please check that one?
> 

Thanks for the fix. The issue could not get reproduced yet, so could not make
much progress on the customer case.

thanks,

> Thanks,
> 
> On 2019/8/7 22:06, Chao Yu wrote:
> > On 2019-8-7 21:40, 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. Currently, add this logic under
> >> CONFIG_F2FS_CHECK_FS to be able to root cause the issue in debug
> >> version.
> >>
> >> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> >> ---
> >> v4: Cover all logic with CONFIG_F2FS_CHECK_FS
> >>
> >>  fs/f2fs/gc.c      | 31 +++++++++++++++++++++++++++++--
> >>  fs/f2fs/segment.c | 14 +++++++++++++-
> >>  fs/f2fs/segment.h |  3 +++
> >>  3 files changed, 45 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >> index 8974672..cbcacbd 100644
> >> --- a/fs/f2fs/gc.c
> >> +++ b/fs/f2fs/gc.c
> >> @@ -382,6 +382,16 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
> >>  			nsearched++;
> >>  		}
> >>  
> >> +#ifdef CONFIG_F2FS_CHECK_FS
> >> +		/*
> >> +		 * skip selecting the invalid segno (that is failed due to block
> >> +		 * validity check failure during GC) to avoid endless GC loop in
> >> +		 * such cases.
> >> +		 */
> >> +		if (test_bit(segno, sm->invalid_segmap))
> >> +			goto next;
> >> +#endif
> >> +
> >>  		secno = GET_SEC_FROM_SEG(sbi, segno);
> >>  
> >>  		if (sec_usage_check(sbi, secno))
> >> @@ -602,8 +612,15 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >>  {
> >>  	struct page *node_page;
> >>  	nid_t nid;
> >> -	unsigned int ofs_in_node;
> >> +	unsigned int ofs_in_node, segno;
> >>  	block_t source_blkaddr;
> >> +	unsigned long offset;
> >> +#ifdef CONFIG_F2FS_CHECK_FS
> >> +	struct sit_info *sit_i = SIT_I(sbi);
> >> +#endif
> >> +
> >> +	segno = GET_SEGNO(sbi, blkaddr);
> >> +	offset = GET_BLKOFF_FROM_SEG0(sbi, blkaddr);
> >>  
> >>  	nid = le32_to_cpu(sum->nid);
> >>  	ofs_in_node = le16_to_cpu(sum->ofs_in_node);
> >> @@ -627,8 +644,18 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >>  	source_blkaddr = datablock_addr(NULL, node_page, ofs_in_node);
> >>  	f2fs_put_page(node_page, 1);
> >>  
> >> -	if (source_blkaddr != blkaddr)
> >> +	if (source_blkaddr != blkaddr) {
> >> +#ifdef CONFIG_F2FS_CHECK_FS
> > 
> > 		unsigned int segno = GET_SEGNO(sbi, blkaddr);
> > 		unsigned int offset = GET_BLKOFF_FROM_SEG0(sbi, blkaddr);
> > 
> > Should be local, otherwise it looks good to me, I think Jaegeuk can help to fix
> > this while merging.
> > 
> > Reviewed-by: Chao Yu <yuchao0@huawei.com>
> > 
> > Thanks,
> > 
> >> +		if (unlikely(check_valid_map(sbi, segno, offset))) {
> >> +			if (!test_and_set_bit(segno, sit_i->invalid_segmap)) {
> >> +				f2fs_err(sbi, "mismatched blkaddr %u (source_blkaddr %u) in seg %u\n",
> >> +						blkaddr, source_blkaddr, segno);
> >> +				f2fs_bug_on(sbi, 1);
> >> +			}
> >> +		}
> >> +#endif
> >>  		return false;
> >> +	}
> >>  	return true;
> >>  }
> >>  
> >> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >> index a661ac3..ee795b1 100644
> >> --- a/fs/f2fs/segment.c
> >> +++ b/fs/f2fs/segment.c
> >> @@ -806,6 +806,9 @@ static void __remove_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
> >>  		enum dirty_type dirty_type)
> >>  {
> >>  	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
> >> +#ifdef CONFIG_F2FS_CHECK_FS
> >> +	struct sit_info *sit_i = SIT_I(sbi);
> >> +#endif
> >>  
> >>  	if (test_and_clear_bit(segno, dirty_i->dirty_segmap[dirty_type]))
> >>  		dirty_i->nr_dirty[dirty_type]--;
> >> @@ -817,9 +820,13 @@ static void __remove_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
> >>  		if (test_and_clear_bit(segno, dirty_i->dirty_segmap[t]))
> >>  			dirty_i->nr_dirty[t]--;
> >>  
> >> -		if (get_valid_blocks(sbi, segno, true) == 0)
> >> +		if (get_valid_blocks(sbi, segno, true) == 0) {
> >>  			clear_bit(GET_SEC_FROM_SEG(sbi, segno),
> >>  						dirty_i->victim_secmap);
> >> +#ifdef CONFIG_F2FS_CHECK_FS
> >> +			clear_bit(segno, sit_i->invalid_segmap);
> >> +#endif
> >> +		}
> >>  	}
> >>  }
> >>  
> >> @@ -4015,6 +4022,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
> >>  	sit_i->sit_bitmap_mir = kmemdup(src_bitmap, bitmap_size, GFP_KERNEL);
> >>  	if (!sit_i->sit_bitmap_mir)
> >>  		return -ENOMEM;
> >> +
> >> +	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
> >> +	if (!sit_i->invalid_segmap)
> >> +		return -ENOMEM;
> >>  #endif
> >>  
> >>  	/* init SIT information */
> >> @@ -4517,6 +4528,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
> >>  	kvfree(sit_i->sit_bitmap);
> >>  #ifdef CONFIG_F2FS_CHECK_FS
> >>  	kvfree(sit_i->sit_bitmap_mir);
> >> +	kvfree(sit_i->invalid_segmap);
> >>  #endif
> >>  	kvfree(sit_i);
> >>  }
> >> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> >> index b746028..9370d53 100644
> >> --- a/fs/f2fs/segment.h
> >> +++ b/fs/f2fs/segment.h
> >> @@ -229,6 +229,9 @@ struct sit_info {
> >>  	char *sit_bitmap;		/* SIT bitmap pointer */
> >>  #ifdef CONFIG_F2FS_CHECK_FS
> >>  	char *sit_bitmap_mir;		/* SIT bitmap mirror */
> >> +
> >> +	/* bitmap of segments to be ignored by GC in case of errors */
> >> +	unsigned long *invalid_segmap;
> >>  #endif
> >>  	unsigned int bitmap_size;	/* SIT bitmap size */
> >>  
> >>
> > .
> > 

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