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Date: Tue, 5 Jan 2016 09:57:55 -0800
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao2.yu@...sung.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 2/3] f2fs: cover more area with nat_tree_lock
Hi Chao,
On Tue, Jan 05, 2016 at 05:33:31PM +0800, Chao Yu wrote:
> Hi Jaegeuk,
>
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> > Sent: Sunday, January 03, 2016 9:26 AM
> > To: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
> > linux-f2fs-devel@...ts.sourceforge.net
> > Cc: Jaegeuk Kim
> > Subject: [f2fs-dev] [PATCH 2/3] f2fs: cover more area with nat_tree_lock
> >
> > There was a subtle bug on nat cache management which incurs wrong nid allocation
> > or wrong block addresses when try_to_free_nats is triggered heavily.
> > This patch enlarges the previous coverage of nat_tree_lock to avoid data race.
>
> Have you figured out how this happen? I'm curious about this issue,
> since still I can't reproduce it and find any clue by reviewing code
> so far.
It's very very subtle bug. I got one panic after 2-days fsstress execution with
flushing caches very frequently.
The possible scenario was to mix a lot of directory operations, f2fs's shrinking
path, and fsyncing files.
And, the suspicious functions are
- try_to_free_nats,
- f2fs_find_entry->get_node_page->get_node_info->cache_nat_entry
- fsync->checkpoint->flush_nat_entries
- build_free_nids
I guess there is somewhat data race to grab and release nat cache entries when
flush_nat_entries is doing, since f2fs_find_entry is not covered by
f2fs_lock_op.
A good thing is that, with this patch, I couldn't get any bug again for 4 days;
still running tho.
Nevertheless, I couldn't describe this precisely, since I couldn't specify the
real root-cause.
Thanks,
>
> Thanks,
>
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> > fs/f2fs/node.c | 29 ++++++++++++-----------------
> > 1 file changed, 12 insertions(+), 17 deletions(-)
> >
> > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > index 669c44e..4dab09f 100644
> > --- a/fs/f2fs/node.c
> > +++ b/fs/f2fs/node.c
> > @@ -262,13 +262,11 @@ static void cache_nat_entry(struct f2fs_nm_info *nm_i, nid_t nid,
> > {
> > struct nat_entry *e;
> >
> > - down_write(&nm_i->nat_tree_lock);
> > e = __lookup_nat_cache(nm_i, nid);
> > if (!e) {
> > e = grab_nat_entry(nm_i, nid);
> > node_info_from_raw_nat(&e->ni, ne);
> > }
> > - up_write(&nm_i->nat_tree_lock);
> > }
> >
> > static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
> > @@ -380,6 +378,8 @@ void get_node_info(struct f2fs_sb_info *sbi, nid_t nid, struct node_info
> > *ni)
> >
> > memset(&ne, 0, sizeof(struct f2fs_nat_entry));
> >
> > + down_write(&nm_i->nat_tree_lock);
> > +
> > /* Check current segment summary */
> > mutex_lock(&curseg->curseg_mutex);
> > i = lookup_journal_in_cursum(sum, NAT_JOURNAL, nid, 0);
> > @@ -400,6 +400,7 @@ void get_node_info(struct f2fs_sb_info *sbi, nid_t nid, struct node_info
> > *ni)
> > cache:
> > /* cache nat entry */
> > cache_nat_entry(NM_I(sbi), nid, &ne);
> > + up_write(&nm_i->nat_tree_lock);
> > }
> >
> > /*
> > @@ -1459,13 +1460,10 @@ static int add_free_nid(struct f2fs_sb_info *sbi, nid_t nid, bool build)
> >
> > if (build) {
> > /* do not add allocated nids */
> > - down_read(&nm_i->nat_tree_lock);
> > ne = __lookup_nat_cache(nm_i, nid);
> > - if (ne &&
> > - (!get_nat_flag(ne, IS_CHECKPOINTED) ||
> > + if (ne && (!get_nat_flag(ne, IS_CHECKPOINTED) ||
> > nat_get_blkaddr(ne) != NULL_ADDR))
> > allocated = true;
> > - up_read(&nm_i->nat_tree_lock);
> > if (allocated)
> > return 0;
> > }
> > @@ -1551,6 +1549,8 @@ static void build_free_nids(struct f2fs_sb_info *sbi)
> > ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nid), FREE_NID_PAGES,
> > META_NAT, true);
> >
> > + down_read(&nm_i->nat_tree_lock);
> > +
> > while (1) {
> > struct page *page = get_current_nat_page(sbi, nid);
> >
> > @@ -1579,6 +1579,7 @@ static void build_free_nids(struct f2fs_sb_info *sbi)
> > remove_free_nid(nm_i, nid);
> > }
> > mutex_unlock(&curseg->curseg_mutex);
> > + up_read(&nm_i->nat_tree_lock);
> >
> > ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nm_i->next_scan_nid),
> > nm_i->ra_nid_pages, META_NAT, false);
> > @@ -1861,14 +1862,12 @@ static void remove_nats_in_journal(struct f2fs_sb_info *sbi)
> >
> > raw_ne = nat_in_journal(sum, i);
> >
> > - down_write(&nm_i->nat_tree_lock);
> > ne = __lookup_nat_cache(nm_i, nid);
> > if (!ne) {
> > ne = grab_nat_entry(nm_i, nid);
> > node_info_from_raw_nat(&ne->ni, &raw_ne);
> > }
> > __set_nat_cache_dirty(nm_i, ne);
> > - up_write(&nm_i->nat_tree_lock);
> > }
> > update_nats_in_cursum(sum, -i);
> > mutex_unlock(&curseg->curseg_mutex);
> > @@ -1902,7 +1901,6 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
> > struct f2fs_nat_block *nat_blk;
> > struct nat_entry *ne, *cur;
> > struct page *page = NULL;
> > - struct f2fs_nm_info *nm_i = NM_I(sbi);
> >
> > /*
> > * there are two steps to flush nat entries:
> > @@ -1939,12 +1937,8 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
> > raw_ne = &nat_blk->entries[nid - start_nid];
> > }
> > raw_nat_from_node_info(raw_ne, &ne->ni);
> > -
> > - down_write(&NM_I(sbi)->nat_tree_lock);
> > nat_reset_flag(ne);
> > __clear_nat_cache_dirty(NM_I(sbi), ne);
> > - up_write(&NM_I(sbi)->nat_tree_lock);
> > -
> > if (nat_get_blkaddr(ne) == NULL_ADDR)
> > add_free_nid(sbi, nid, false);
> > }
> > @@ -1956,9 +1950,7 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
> >
> > f2fs_bug_on(sbi, set->entry_cnt);
> >
> > - down_write(&nm_i->nat_tree_lock);
> > radix_tree_delete(&NM_I(sbi)->nat_set_root, set->set);
> > - up_write(&nm_i->nat_tree_lock);
> > kmem_cache_free(nat_entry_set_slab, set);
> > }
> >
> > @@ -1978,6 +1970,9 @@ void flush_nat_entries(struct f2fs_sb_info *sbi)
> >
> > if (!nm_i->dirty_nat_cnt)
> > return;
> > +
> > + down_write(&nm_i->nat_tree_lock);
> > +
> > /*
> > * if there are no enough space in journal to store dirty nat
> > * entries, remove all entries from journal and merge them
> > @@ -1986,7 +1981,6 @@ void flush_nat_entries(struct f2fs_sb_info *sbi)
> > if (!__has_cursum_space(sum, nm_i->dirty_nat_cnt, NAT_JOURNAL))
> > remove_nats_in_journal(sbi);
> >
> > - down_write(&nm_i->nat_tree_lock);
> > while ((found = __gang_lookup_nat_set(nm_i,
> > set_idx, SETVEC_SIZE, setvec))) {
> > unsigned idx;
> > @@ -1995,12 +1989,13 @@ void flush_nat_entries(struct f2fs_sb_info *sbi)
> > __adjust_nat_entry_set(setvec[idx], &sets,
> > MAX_NAT_JENTRIES(sum));
> > }
> > - up_write(&nm_i->nat_tree_lock);
> >
> > /* flush dirty nats in nat entry set */
> > list_for_each_entry_safe(set, tmp, &sets, set_list)
> > __flush_nat_entry_set(sbi, set);
> >
> > + up_write(&nm_i->nat_tree_lock);
> > +
> > f2fs_bug_on(sbi, nm_i->dirty_nat_cnt);
> > }
> >
> > --
> > 2.6.3
> >
> >
> > ------------------------------------------------------------------------------
> > _______________________________________________
> > Linux-f2fs-devel mailing list
> > Linux-f2fs-devel@...ts.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
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