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authorRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>2015-02-05 23:25:20 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-06 00:35:29 +0300
commit7ef3ff2fea8bf5e4a21cef47ad87710a3d0fdb52 (patch)
treefae90c5009ed6bf5009cedf9646c0a4edd71304c /fs/nilfs2/segment.c
parent81cca6fb1271b91f06b008976ea132bec2f14d86 (diff)
downloadlinux-7ef3ff2fea8bf5e4a21cef47ad87710a3d0fdb52.tar.xz
nilfs2: fix deadlock of segment constructor over I_SYNC flag
Nilfs2 eventually hangs in a stress test with fsstress program. This issue was caused by the following deadlock over I_SYNC flag between nilfs_segctor_thread() and writeback_sb_inodes(): nilfs_segctor_thread() nilfs_segctor_thread_construct() nilfs_segctor_unlock() nilfs_dispose_list() iput() iput_final() evict() inode_wait_for_writeback() * wait for I_SYNC flag writeback_sb_inodes() * set I_SYNC flag on inode->i_state __writeback_single_inode() do_writepages() nilfs_writepages() nilfs_construct_dsync_segment() nilfs_segctor_sync() * wait for completion of segment constructor inode_sync_complete() * clear I_SYNC flag after __writeback_single_inode() completed writeback_sb_inodes() calls do_writepages() for dirty inodes after setting I_SYNC flag on inode->i_state. do_writepages() in turn calls nilfs_writepages(), which can run segment constructor and wait for its completion. On the other hand, segment constructor calls iput(), which can call evict() and wait for the I_SYNC flag on inode_wait_for_writeback(). Since segment constructor doesn't know when I_SYNC will be set, it cannot know whether iput() will block or not unless inode->i_nlink has a non-zero count. We can prevent evict() from being called in iput() by implementing sop->drop_inode(), but it's not preferable to leave inodes with i_nlink == 0 for long periods because it even defers file truncation and inode deallocation. So, this instead resolves the deadlock by calling iput() asynchronously with a workqueue for inodes with i_nlink == 0. Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp> Cc: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/nilfs2/segment.c')
-rw-r--r--fs/nilfs2/segment.c44
1 files changed, 39 insertions, 5 deletions
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 7ef18fc656c2..469086b9f99b 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -305,7 +305,6 @@ static void nilfs_transaction_lock(struct super_block *sb,
ti->ti_count = 0;
ti->ti_save = cur_ti;
ti->ti_magic = NILFS_TI_MAGIC;
- INIT_LIST_HEAD(&ti->ti_garbage);
current->journal_info = ti;
for (;;) {
@@ -332,8 +331,6 @@ static void nilfs_transaction_unlock(struct super_block *sb)
up_write(&nilfs->ns_segctor_sem);
current->journal_info = ti->ti_save;
- if (!list_empty(&ti->ti_garbage))
- nilfs_dispose_list(nilfs, &ti->ti_garbage, 0);
}
static void *nilfs_segctor_map_segsum_entry(struct nilfs_sc_info *sci,
@@ -746,6 +743,15 @@ static void nilfs_dispose_list(struct the_nilfs *nilfs,
}
}
+static void nilfs_iput_work_func(struct work_struct *work)
+{
+ struct nilfs_sc_info *sci = container_of(work, struct nilfs_sc_info,
+ sc_iput_work);
+ struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+
+ nilfs_dispose_list(nilfs, &sci->sc_iput_queue, 0);
+}
+
static int nilfs_test_metadata_dirty(struct the_nilfs *nilfs,
struct nilfs_root *root)
{
@@ -1900,8 +1906,8 @@ static int nilfs_segctor_collect_dirty_files(struct nilfs_sc_info *sci,
static void nilfs_segctor_drop_written_files(struct nilfs_sc_info *sci,
struct the_nilfs *nilfs)
{
- struct nilfs_transaction_info *ti = current->journal_info;
struct nilfs_inode_info *ii, *n;
+ int defer_iput = false;
spin_lock(&nilfs->ns_inode_lock);
list_for_each_entry_safe(ii, n, &sci->sc_dirty_files, i_dirty) {
@@ -1912,9 +1918,24 @@ static void nilfs_segctor_drop_written_files(struct nilfs_sc_info *sci,
clear_bit(NILFS_I_BUSY, &ii->i_state);
brelse(ii->i_bh);
ii->i_bh = NULL;
- list_move_tail(&ii->i_dirty, &ti->ti_garbage);
+ list_del_init(&ii->i_dirty);
+ if (!ii->vfs_inode.i_nlink) {
+ /*
+ * Defer calling iput() to avoid a deadlock
+ * over I_SYNC flag for inodes with i_nlink == 0
+ */
+ list_add_tail(&ii->i_dirty, &sci->sc_iput_queue);
+ defer_iput = true;
+ } else {
+ spin_unlock(&nilfs->ns_inode_lock);
+ iput(&ii->vfs_inode);
+ spin_lock(&nilfs->ns_inode_lock);
+ }
}
spin_unlock(&nilfs->ns_inode_lock);
+
+ if (defer_iput)
+ schedule_work(&sci->sc_iput_work);
}
/*
@@ -2583,6 +2604,8 @@ static struct nilfs_sc_info *nilfs_segctor_new(struct super_block *sb,
INIT_LIST_HEAD(&sci->sc_segbufs);
INIT_LIST_HEAD(&sci->sc_write_logs);
INIT_LIST_HEAD(&sci->sc_gc_inodes);
+ INIT_LIST_HEAD(&sci->sc_iput_queue);
+ INIT_WORK(&sci->sc_iput_work, nilfs_iput_work_func);
init_timer(&sci->sc_timer);
sci->sc_interval = HZ * NILFS_SC_DEFAULT_TIMEOUT;
@@ -2609,6 +2632,8 @@ static void nilfs_segctor_write_out(struct nilfs_sc_info *sci)
ret = nilfs_segctor_construct(sci, SC_LSEG_SR);
nilfs_transaction_unlock(sci->sc_super);
+ flush_work(&sci->sc_iput_work);
+
} while (ret && retrycount-- > 0);
}
@@ -2633,6 +2658,9 @@ static void nilfs_segctor_destroy(struct nilfs_sc_info *sci)
|| sci->sc_seq_request != sci->sc_seq_done);
spin_unlock(&sci->sc_state_lock);
+ if (flush_work(&sci->sc_iput_work))
+ flag = true;
+
if (flag || !nilfs_segctor_confirm(sci))
nilfs_segctor_write_out(sci);
@@ -2642,6 +2670,12 @@ static void nilfs_segctor_destroy(struct nilfs_sc_info *sci)
nilfs_dispose_list(nilfs, &sci->sc_dirty_files, 1);
}
+ if (!list_empty(&sci->sc_iput_queue)) {
+ nilfs_warning(sci->sc_super, __func__,
+ "iput queue is not empty\n");
+ nilfs_dispose_list(nilfs, &sci->sc_iput_queue, 1);
+ }
+
WARN_ON(!list_empty(&sci->sc_segbufs));
WARN_ON(!list_empty(&sci->sc_write_logs));