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authorChao Yu <yuchao0@huawei.com>2017-07-22 03:52:23 +0300
committerJaegeuk Kim <jaegeuk@kernel.org>2017-08-01 02:47:27 +0300
commitdc6febb6bcec7ff1b4a4d306411013b5f648f27e (patch)
treea0b22fadbd8c2e8332fc358b0b31f1c1fa26b073 /fs/f2fs/gc.c
parent7a10f0177e117e9935ee9e5c595fcf3c57215de5 (diff)
downloadlinux-dc6febb6bcec7ff1b4a4d306411013b5f648f27e.tar.xz
f2fs: make background threads of f2fs being aware of freezing
When ->freeze_fs is called from lvm for doing snapshot, it needs to make sure there will be no more changes in filesystem's data, however, previously, background threads like GC thread wasn't aware of freezing, so in environment with active background threads, data of snapshot becomes unstable. This patch fixes this issue by adding sb_{start,end}_intwrite in below background threads: - GC thread - flush thread - discard thread Note that, don't use sb_start_intwrite() in gc_thread_func() due to: generic/241 reports below bug: ====================================================== WARNING: possible circular locking dependency detected 4.13.0-rc1+ #32 Tainted: G O ------------------------------------------------------ f2fs_gc-250:0/22186 is trying to acquire lock: (&sbi->gc_mutex){+.+...}, at: [<f8fa7f0b>] f2fs_sync_fs+0x7b/0x1b0 [f2fs] but task is already holding lock: (sb_internal#2){++++.-}, at: [<f8fb5609>] gc_thread_func+0x159/0x4a0 [f2fs] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (sb_internal#2){++++.-}: __lock_acquire+0x405/0x7b0 lock_acquire+0xae/0x220 __sb_start_write+0x11d/0x1f0 f2fs_evict_inode+0x2d6/0x4e0 [f2fs] evict+0xa8/0x170 iput+0x1fb/0x2c0 f2fs_sync_inode_meta+0x3f/0xf0 [f2fs] write_checkpoint+0x1b1/0x750 [f2fs] f2fs_sync_fs+0x85/0x1b0 [f2fs] f2fs_do_sync_file.isra.24+0x137/0xa30 [f2fs] f2fs_sync_file+0x34/0x40 [f2fs] vfs_fsync_range+0x4a/0xa0 do_fsync+0x3c/0x60 SyS_fdatasync+0x15/0x20 do_fast_syscall_32+0xa1/0x1b0 entry_SYSENTER_32+0x4c/0x7b -> #1 (&sbi->cp_mutex){+.+...}: __lock_acquire+0x405/0x7b0 lock_acquire+0xae/0x220 __mutex_lock+0x4f/0x830 mutex_lock_nested+0x25/0x30 write_checkpoint+0x2f/0x750 [f2fs] f2fs_sync_fs+0x85/0x1b0 [f2fs] sync_filesystem+0x67/0x80 generic_shutdown_super+0x27/0x100 kill_block_super+0x22/0x50 kill_f2fs_super+0x3a/0x40 [f2fs] deactivate_locked_super+0x3d/0x70 deactivate_super+0x40/0x60 cleanup_mnt+0x39/0x70 __cleanup_mnt+0x10/0x20 task_work_run+0x69/0x80 exit_to_usermode_loop+0x57/0x92 do_fast_syscall_32+0x18c/0x1b0 entry_SYSENTER_32+0x4c/0x7b -> #0 (&sbi->gc_mutex){+.+...}: validate_chain.isra.36+0xc50/0xdb0 __lock_acquire+0x405/0x7b0 lock_acquire+0xae/0x220 __mutex_lock+0x4f/0x830 mutex_lock_nested+0x25/0x30 f2fs_sync_fs+0x7b/0x1b0 [f2fs] f2fs_balance_fs_bg+0xb9/0x200 [f2fs] gc_thread_func+0x302/0x4a0 [f2fs] kthread+0xe9/0x120 ret_from_fork+0x19/0x24 other info that might help us debug this: Chain exists of: &sbi->gc_mutex --> &sbi->cp_mutex --> sb_internal#2 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(sb_internal#2); lock(&sbi->cp_mutex); lock(sb_internal#2); lock(&sbi->gc_mutex); *** DEADLOCK *** 1 lock held by f2fs_gc-250:0/22186: #0: (sb_internal#2){++++.-}, at: [<f8fb5609>] gc_thread_func+0x159/0x4a0 [f2fs] stack backtrace: CPU: 2 PID: 22186 Comm: f2fs_gc-250:0 Tainted: G O 4.13.0-rc1+ #32 Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 Call Trace: dump_stack+0x5f/0x92 print_circular_bug+0x1b3/0x1bd validate_chain.isra.36+0xc50/0xdb0 ? __this_cpu_preempt_check+0xf/0x20 __lock_acquire+0x405/0x7b0 lock_acquire+0xae/0x220 ? f2fs_sync_fs+0x7b/0x1b0 [f2fs] __mutex_lock+0x4f/0x830 ? f2fs_sync_fs+0x7b/0x1b0 [f2fs] mutex_lock_nested+0x25/0x30 ? f2fs_sync_fs+0x7b/0x1b0 [f2fs] f2fs_sync_fs+0x7b/0x1b0 [f2fs] f2fs_balance_fs_bg+0xb9/0x200 [f2fs] gc_thread_func+0x302/0x4a0 [f2fs] ? preempt_schedule_common+0x2f/0x4d ? f2fs_gc+0x540/0x540 [f2fs] kthread+0xe9/0x120 ? f2fs_gc+0x540/0x540 [f2fs] ? kthread_create_on_node+0x30/0x30 ret_from_fork+0x19/0x24 The deadlock occurs in below condition: GC Thread Thread B - sb_start_intwrite - f2fs_sync_file - f2fs_sync_fs - mutex_lock(&sbi->gc_mutex) - write_checkpoint - block_operations - f2fs_sync_inode_meta - iput - sb_start_intwrite - mutex_lock(&sbi->gc_mutex) Fix this by altering sb_start_intwrite to sb_start_write_trylock. Signed-off-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Diffstat (limited to 'fs/f2fs/gc.c')
-rw-r--r--fs/f2fs/gc.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index fa3d2e2df8e7..41c649c9c55c 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -55,6 +55,9 @@ static int gc_thread_func(void *data)
}
#endif
+ if (!sb_start_write_trylock(sbi->sb))
+ continue;
+
/*
* [GC triggering condition]
* 0. GC is not conducted currently.
@@ -69,12 +72,12 @@ static int gc_thread_func(void *data)
* So, I'd like to wait some time to collect dirty segments.
*/
if (!mutex_trylock(&sbi->gc_mutex))
- continue;
+ goto next;
if (!is_idle(sbi)) {
increase_sleep_time(gc_th, &wait_ms);
mutex_unlock(&sbi->gc_mutex);
- continue;
+ goto next;
}
if (has_enough_invalid_blocks(sbi))
@@ -93,6 +96,8 @@ static int gc_thread_func(void *data)
/* balancing f2fs's metadata periodically */
f2fs_balance_fs_bg(sbi);
+next:
+ sb_end_write(sbi->sb);
} while (!kthread_should_stop());
return 0;