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Date: Wed, 7 Aug 2019 10:44:50 +0530
From: Sahitya Tummala <stummala@...eaurora.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: Jaegeuk Kim <jaegeuk@...nel.org>,
linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, stummala@...eaurora.org
Subject: Re: [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc()
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@...eaurora.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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