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Subject[PATCH] f2fs: fix race condition in between free nid allocator/initializer
Date
In below concurrent case, allocated nid can be loaded into free nid cache
and be allocated again.

Thread A Thread B
- f2fs_create
- f2fs_new_inode
- alloc_nid
- __insert_nid_to_list(ALLOC_NID_LIST)
- f2fs_balance_fs_bg
- build_free_nids
- __build_free_nids
- scan_nat_page
- add_free_nid
- __lookup_nat_cache
- f2fs_add_link
- init_inode_metadata
- new_inode_page
- new_node_page
- set_node_addr
- alloc_nid_done
- __remove_nid_from_list(ALLOC_NID_LIST)
- __insert_nid_to_list(FREE_NID_LIST)

This patch uses build_lock covering free nid allocation and initialization
to avoid this race condition.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
fs/f2fs/node.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 3bfffd744f87..ea45be031c9d 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -22,8 +22,6 @@
#include "trace.h"
#include <trace/events/f2fs.h>

-#define on_build_free_nids(nmi) mutex_is_locked(&nm_i->build_lock)
-
static struct kmem_cache *nat_entry_slab;
static struct kmem_cache *free_nid_slab;
static struct kmem_cache *nat_entry_set_slab;
@@ -1802,6 +1800,7 @@ static void remove_free_nid(struct f2fs_sb_info *sbi, nid_t nid)
struct free_nid *i;
bool need_free = false;

+ mutex_lock(&nm_i->build_lock);
spin_lock(&nm_i->nid_list_lock);
i = __lookup_free_nid_list(nm_i, nid);
if (i && i->state == NID_NEW) {
@@ -1809,6 +1808,7 @@ static void remove_free_nid(struct f2fs_sb_info *sbi, nid_t nid)
need_free = true;
}
spin_unlock(&nm_i->nid_list_lock);
+ mutex_unlock(&nm_i->build_lock);

if (need_free)
kmem_cache_free(free_nid_slab, i);
@@ -1999,15 +1999,18 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
return false;
}
#endif
+
+ mutex_lock(&nm_i->build_lock);
spin_lock(&nm_i->nid_list_lock);

if (unlikely(nm_i->available_nids == 0)) {
spin_unlock(&nm_i->nid_list_lock);
+ mutex_unlock(&nm_i->build_lock);
return false;
}

/* We should not use stale free nids created by build_free_nids */
- if (nm_i->nid_cnt[FREE_NID_LIST] && !on_build_free_nids(nm_i)) {
+ if (nm_i->nid_cnt[FREE_NID_LIST]) {
f2fs_bug_on(sbi, list_empty(&nm_i->nid_list[FREE_NID_LIST]));
i = list_first_entry(&nm_i->nid_list[FREE_NID_LIST],
struct free_nid, list);
@@ -2021,9 +2024,11 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
update_free_nid_bitmap(sbi, *nid, false, false);

spin_unlock(&nm_i->nid_list_lock);
+ mutex_unlock(&nm_i->build_lock);
return true;
}
spin_unlock(&nm_i->nid_list_lock);
+ mutex_unlock(&nm_i->build_lock);

/* Let's scan nat pages and its caches to get free nids */
build_free_nids(sbi, true, false);
@@ -2038,11 +2043,13 @@ void alloc_nid_done(struct f2fs_sb_info *sbi, nid_t nid)
struct f2fs_nm_info *nm_i = NM_I(sbi);
struct free_nid *i;

+ mutex_lock(&nm_i->build_lock);
spin_lock(&nm_i->nid_list_lock);
i = __lookup_free_nid_list(nm_i, nid);
f2fs_bug_on(sbi, !i);
__remove_nid_from_list(sbi, i, ALLOC_NID_LIST, false);
spin_unlock(&nm_i->nid_list_lock);
+ mutex_unlock(&nm_i->build_lock);

kmem_cache_free(free_nid_slab, i);
}
@@ -2059,6 +2066,7 @@ void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
if (!nid)
return;

+ mutex_lock(&nm_i->build_lock);
spin_lock(&nm_i->nid_list_lock);
i = __lookup_free_nid_list(nm_i, nid);
f2fs_bug_on(sbi, !i);
@@ -2077,6 +2085,7 @@ void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
update_free_nid_bitmap(sbi, nid, true, false);

spin_unlock(&nm_i->nid_list_lock);
+ mutex_unlock(&nm_i->build_lock);

if (need_free)
kmem_cache_free(free_nid_slab, i);
@@ -2443,6 +2452,7 @@ void flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
if (!nm_i->dirty_nat_cnt)
return;

+ mutex_lock(&nm_i->build_lock);
down_write(&nm_i->nat_tree_lock);

/*
@@ -2468,6 +2478,7 @@ void flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
__flush_nat_entry_set(sbi, set, cpc);

up_write(&nm_i->nat_tree_lock);
+ mutex_unlock(&nm_i->build_lock);

f2fs_bug_on(sbi, nm_i->dirty_nat_cnt);
}
--
2.8.2.295.g3f1c1d0
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