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Subject[PATCH] vfs: stop shrinker while fs is freezed
Date
Shrinker could be blocked by freeze while dropping the last reference of
some inode that had been removed. As "s_umount" lock was acquired by the
Shrinker before blocked, the thaw will hung by this lock. This caused a
deadlock.

crash7latest> set 132
PID: 132
COMMAND: "kswapd0:0"
TASK: ffff9cdc9dfb5f00 [THREAD_INFO: ffff9cdc9dfb5f00]
CPU: 6
STATE: TASK_UNINTERRUPTIBLE
crash7latest> bt
PID: 132 TASK: ffff9cdc9dfb5f00 CPU: 6 COMMAND: "kswapd0:0"
#0 [ffffaa5d075bf900] __schedule at ffffffff8186487c
#1 [ffffaa5d075bf998] schedule at ffffffff81864e96
#2 [ffffaa5d075bf9b0] rwsem_down_read_failed at ffffffff818689ee
#3 [ffffaa5d075bfa40] call_rwsem_down_read_failed at ffffffff81859308
#4 [ffffaa5d075bfa90] __percpu_down_read at ffffffff810ebd38
#5 [ffffaa5d075bfab0] __sb_start_write at ffffffff812859ef
#6 [ffffaa5d075bfad0] xfs_trans_alloc at ffffffffc07ebe9c [xfs]
#7 [ffffaa5d075bfb18] xfs_free_eofblocks at ffffffffc07c39d1 [xfs]
#8 [ffffaa5d075bfb80] xfs_inactive at ffffffffc07de878 [xfs]
#9 [ffffaa5d075bfba0] __dta_xfs_fs_destroy_inode_3543 at ffffffffc07e885e [xfs]
#10 [ffffaa5d075bfbd0] destroy_inode at ffffffff812a25de
#11 [ffffaa5d075bfbe8] evict at ffffffff812a2b73
#12 [ffffaa5d075bfc10] dispose_list at ffffffff812a2c1d
#13 [ffffaa5d075bfc38] prune_icache_sb at ffffffff812a421a
#14 [ffffaa5d075bfc70] super_cache_scan at ffffffff812870a1
#15 [ffffaa5d075bfcc8] shrink_slab at ffffffff811eebb3
#16 [ffffaa5d075bfdb0] shrink_node at ffffffff811f4788
#17 [ffffaa5d075bfe38] kswapd at ffffffff811f58c3
#18 [ffffaa5d075bff08] kthread at ffffffff810b75d5
#19 [ffffaa5d075bff50] ret_from_fork at ffffffff81a0035e
crash7latest> set 31060
PID: 31060
COMMAND: "safefreeze"
TASK: ffff9cd292868000 [THREAD_INFO: ffff9cd292868000]
CPU: 2
STATE: TASK_UNINTERRUPTIBLE
crash7latest> bt
PID: 31060 TASK: ffff9cd292868000 CPU: 2 COMMAND: "safefreeze"
#0 [ffffaa5d10047c90] __schedule at ffffffff8186487c
#1 [ffffaa5d10047d28] schedule at ffffffff81864e96
#2 [ffffaa5d10047d40] rwsem_down_write_failed at ffffffff81868f18
#3 [ffffaa5d10047dd8] call_rwsem_down_write_failed at ffffffff81859367
#4 [ffffaa5d10047e20] down_write at ffffffff81867cfd
#5 [ffffaa5d10047e38] thaw_super at ffffffff81285d2d
#6 [ffffaa5d10047e60] do_vfs_ioctl at ffffffff81299566
#7 [ffffaa5d10047ee8] sys_ioctl at ffffffff81299709
#8 [ffffaa5d10047f28] do_syscall_64 at ffffffff81003949
#9 [ffffaa5d10047f50] entry_SYSCALL_64_after_hwframe at ffffffff81a001ad
RIP: 0000000000453d67 RSP: 00007ffff9c1ce78 RFLAGS: 00000206
RAX: ffffffffffffffda RBX: 0000000001cbe92c RCX: 0000000000453d67
RDX: 0000000000000000 RSI: 00000000c0045878 RDI: 0000000000000014
RBP: 00007ffff9c1cf80 R8: 0000000000000000 R9: 0000000000000012
R10: 0000000000000008 R11: 0000000000000206 R12: 0000000000401fb0
R13: 0000000000402040 R14: 0000000000000000 R15: 0000000000000000
ORIG_RAX: 0000000000000010 CS: 0033 SS: 002b

Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
---
fs/super.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index cfadab2cbf35..adc18652302b 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -80,6 +80,11 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
if (!trylock_super(sb))
return SHRINK_STOP;

+ if (sb->s_writers.frozen != SB_UNFROZEN) {
+ up_read(&sb->s_umount);
+ return SHRINK_STOP;
+ }
+
if (sb->s_op->nr_cached_objects)
fs_objects = sb->s_op->nr_cached_objects(sb, sc);

--
2.17.1
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