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    SubjectRe: [PATCH] f2fs: prevent meta updates while checkpoint is in progress
    On 04/01, Chao Yu wrote:
    > On 2020/4/1 2:43, Jaegeuk Kim wrote:
    > > On 03/31, Sahitya Tummala wrote:
    > >> On Mon, Mar 30, 2020 at 08:54:19PM -0700, Jaegeuk Kim wrote:
    > >>> On 03/26, Sahitya Tummala wrote:
    > >>>> allocate_segment_for_resize() can cause metapage updates if
    > >>>> it requires to change the current node/data segments for resizing.
    > >>>> Stop these meta updates when there is a checkpoint already
    > >>>> in progress to prevent inconsistent CP data.
    > >>>
    > >>> I'd prefer to use f2fs_lock_op() in bigger coverage.
    > >>
    > >> Do you mean to cover the entire free_segment_range() function within
    > >> f2fs_lock_op()? Please clarify.
    > >
    > > I didn't test tho, something like this?
    > >
    > > ---
    > > fs/f2fs/checkpoint.c | 6 ++++--
    > > fs/f2fs/f2fs.h | 2 +-
    > > fs/f2fs/gc.c | 28 ++++++++++++++--------------
    > > fs/f2fs/super.c | 1 -
    > > include/trace/events/f2fs.h | 4 +++-
    > > 5 files changed, 22 insertions(+), 19 deletions(-)
    > >
    > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
    > > index 852890b72d6ac..531995192b714 100644
    > > --- a/fs/f2fs/checkpoint.c
    > > +++ b/fs/f2fs/checkpoint.c
    > > @@ -1553,7 +1553,8 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
    > > return 0;
    > > f2fs_warn(sbi, "Start checkpoint disabled!");
    > > }
    > > - mutex_lock(&sbi->cp_mutex);
    > > + if (cpc->reason != CP_RESIZE)
    > > + mutex_lock(&sbi->cp_mutex);
    > >
    > > if (!is_sbi_flag_set(sbi, SBI_IS_DIRTY) &&
    > > ((cpc->reason & CP_FASTBOOT) || (cpc->reason & CP_SYNC) ||
    > > @@ -1622,7 +1623,8 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
    > > f2fs_update_time(sbi, CP_TIME);
    > > trace_f2fs_write_checkpoint(sbi->sb, cpc->reason, "finish checkpoint");
    > > out:
    > > - mutex_unlock(&sbi->cp_mutex);
    > > + if (cpc->reason != CP_RESIZE)
    > > + mutex_unlock(&sbi->cp_mutex);
    > > return err;
    > > }
    > >
    > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
    > > index c84442eefc56d..7c98dca3ec1d6 100644
    > > --- a/fs/f2fs/f2fs.h
    > > +++ b/fs/f2fs/f2fs.h
    > > @@ -193,6 +193,7 @@ enum {
    > > #define CP_DISCARD 0x00000010
    > > #define CP_TRIMMED 0x00000020
    > > #define CP_PAUSE 0x00000040
    > > +#define CP_RESIZE 0x00000080
    > >
    > > #define MAX_DISCARD_BLOCKS(sbi) BLKS_PER_SEC(sbi)
    > > #define DEF_MAX_DISCARD_REQUEST 8 /* issue 8 discards per round */
    > > @@ -1417,7 +1418,6 @@ struct f2fs_sb_info {
    > > unsigned int segs_per_sec; /* segments per section */
    > > unsigned int secs_per_zone; /* sections per zone */
    > > unsigned int total_sections; /* total section count */
    > > - struct mutex resize_mutex; /* for resize exclusion */
    > > unsigned int total_node_count; /* total node block count */
    > > unsigned int total_valid_node_count; /* valid node block count */
    > > loff_t max_file_blocks; /* max block index of file */
    > > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
    > > index 26248c8936db0..1e5a06fda09d3 100644
    > > --- a/fs/f2fs/gc.c
    > > +++ b/fs/f2fs/gc.c
    > > @@ -1402,8 +1402,9 @@ void f2fs_build_gc_manager(struct f2fs_sb_info *sbi)
    > > static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
    > > unsigned int end)
    > > {
    > > - int type;
    > > unsigned int segno, next_inuse;
    > > + struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
    > > + int type;
    > > int err = 0;
    > >
    > > /* Move out cursegs from the target range */
    > > @@ -1417,16 +1418,14 @@ static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
    > > .iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
    > > };
    > >
    > > - down_write(&sbi->gc_lock);
    > > do_garbage_collect(sbi, segno, &gc_list, FG_GC);
    > > - up_write(&sbi->gc_lock);
    > > put_gc_inode(&gc_list);
    > >
    > > if (get_valid_blocks(sbi, segno, true))
    > > return -EAGAIN;
    > > }
    > >
    > > - err = f2fs_sync_fs(sbi->sb, 1);
    > > + err = f2fs_write_checkpoint(sbi, &cpc);
    > > if (err)
    > > return err;
    > >
    > > @@ -1502,6 +1501,7 @@ static void update_fs_metadata(struct f2fs_sb_info *sbi, int secs)
    > > int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
    > > {
    > > __u64 old_block_count, shrunk_blocks;
    > > + struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
    > > unsigned int secs;
    > > int gc_mode, gc_type;
    > > int err = 0;
    > > @@ -1538,7 +1538,9 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
    > > return -EINVAL;
    > > }
    > >
    > > - freeze_bdev(sbi->sb->s_bdev);
    > > + freeze_super(sbi->sb);
    >
    > Look at this again, I guess holding freeze lock here may cause potential
    > hang task issue, imaging that in a low-end storage, shrinking large size
    > address space, free_segment_range() needs very long time to migrate all
    > valid blocks in the tail of device, that's why previously we do block
    > migration with small gc_lock coverage.

    Hmm, it seems we had to do like:
    1) do GC
    2) freeze everything
    3) check it's okay to go new metadata
    4) do resize
    5) thaw

    >
    > Quoted:
    >
    > Changelog v5 ==> v6:
    > - In free_segment_range(), reduce granularity of gc_mutex.
    >
    > Thanks,
    >
    > > + down_write(&sbi->gc_lock);
    > > + mutex_lock(&sbi->cp_mutex);
    > >
    > > shrunk_blocks = old_block_count - block_count;
    > > secs = div_u64(shrunk_blocks, BLKS_PER_SEC(sbi));
    > > @@ -1551,11 +1553,12 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
    > > sbi->user_block_count -= shrunk_blocks;
    > > spin_unlock(&sbi->stat_lock);
    > > if (err) {
    > > - thaw_bdev(sbi->sb->s_bdev, sbi->sb);
    > > + mutex_unlock(&sbi->cp_mutex);
    > > + up_write(&sbi->gc_lock);
    > > + thaw_super(sbi->sb);
    > > return err;
    > > }
    > >
    > > - mutex_lock(&sbi->resize_mutex);
    > > set_sbi_flag(sbi, SBI_IS_RESIZEFS);
    > >
    > > mutex_lock(&DIRTY_I(sbi)->seglist_lock);
    > > @@ -1587,17 +1590,13 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
    > > goto out;
    > > }
    > >
    > > - mutex_lock(&sbi->cp_mutex);
    > > update_fs_metadata(sbi, -secs);
    > > clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
    > > set_sbi_flag(sbi, SBI_IS_DIRTY);
    > > - mutex_unlock(&sbi->cp_mutex);
    > >
    > > - err = f2fs_sync_fs(sbi->sb, 1);
    > > + err = f2fs_write_checkpoint(sbi, &cpc);
    > > if (err) {
    > > - mutex_lock(&sbi->cp_mutex);
    > > update_fs_metadata(sbi, secs);
    > > - mutex_unlock(&sbi->cp_mutex);
    > > update_sb_metadata(sbi, secs);
    > > f2fs_commit_super(sbi, false);
    > > }
    > > @@ -1612,7 +1611,8 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
    > > spin_unlock(&sbi->stat_lock);
    > > }
    > > clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
    > > - mutex_unlock(&sbi->resize_mutex);
    > > - thaw_bdev(sbi->sb->s_bdev, sbi->sb);
    > > + mutex_unlock(&sbi->cp_mutex);
    > > + up_write(&sbi->gc_lock);
    > > + thaw_super(sbi->sb);
    > > return err;
    > > }
    > > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
    > > index b83b17b54a0a6..1e7b1d21d0177 100644
    > > --- a/fs/f2fs/super.c
    > > +++ b/fs/f2fs/super.c
    > > @@ -3412,7 +3412,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
    > > init_rwsem(&sbi->gc_lock);
    > > mutex_init(&sbi->writepages);
    > > mutex_init(&sbi->cp_mutex);
    > > - mutex_init(&sbi->resize_mutex);
    > > init_rwsem(&sbi->node_write);
    > > init_rwsem(&sbi->node_change);
    > >
    > > diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
    > > index d97adfc327f03..f5eb03c54e96f 100644
    > > --- a/include/trace/events/f2fs.h
    > > +++ b/include/trace/events/f2fs.h
    > > @@ -50,6 +50,7 @@ TRACE_DEFINE_ENUM(CP_RECOVERY);
    > > TRACE_DEFINE_ENUM(CP_DISCARD);
    > > TRACE_DEFINE_ENUM(CP_TRIMMED);
    > > TRACE_DEFINE_ENUM(CP_PAUSE);
    > > +TRACE_DEFINE_ENUM(CP_RESIZE);
    > >
    > > #define show_block_type(type) \
    > > __print_symbolic(type, \
    > > @@ -126,7 +127,8 @@ TRACE_DEFINE_ENUM(CP_PAUSE);
    > > { CP_RECOVERY, "Recovery" }, \
    > > { CP_DISCARD, "Discard" }, \
    > > { CP_PAUSE, "Pause" }, \
    > > - { CP_TRIMMED, "Trimmed" })
    > > + { CP_TRIMMED, "Trimmed" }, \
    > > + { CP_RESIZE, "Resize" })
    > >
    > > #define show_fsync_cpreason(type) \
    > > __print_symbolic(type, \
    > >

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