We did a test to delete a large number of files when the memory
was insufficient, and then A deadlock problem was found.
[ 1240.279183] -> #1 (fs_reclaim){+.+.}-{0:0}:
[ 1240.280450] lock_acquire+0x197/0x460
[ 1240.281548] fs_reclaim_acquire.part.0+0x20/0x30
[ 1240.282625] kmem_cache_alloc+0x2b/0x940
[ 1240.283816] xfs_trans_alloc+0x8a/0x8b0
[ 1240.284757] xfs_inactive_ifree+0xe4/0x4e0
[ 1240.285935] xfs_inactive+0x4e9/0x8a0
[ 1240.286836] xfs_inodegc_worker+0x160/0x5e0
[ 1240.287969] process_one_work+0xa19/0x16b0
[ 1240.289030] worker_thread+0x9e/0x1050
[ 1240.290131] kthread+0x34f/0x460
[ 1240.290999] ret_from_fork+0x22/0x30
[ 1240.291905]
[ 1240.291905] -> #0 ((work_completion)(&gc->work)){+.+.}-{0:0}:
[ 1240.293569] check_prev_add+0x160/0x2490
[ 1240.294473] __lock_acquire+0x2c4d/0x5160
[ 1240.295544] lock_acquire+0x197/0x460
[ 1240.296403] __flush_work+0x6bc/0xa20
[ 1240.297522] xfs_inode_mark_reclaimable+0x6f0/0xdc0
[ 1240.298649] destroy_inode+0xc6/0x1b0
[ 1240.299677] dispose_list+0xe1/0x1d0
[ 1240.300567] prune_icache_sb+0xec/0x150
[ 1240.301794] super_cache_scan+0x2c9/0x480
[ 1240.302776] do_shrink_slab+0x3f0/0xaa0
[ 1240.303671] shrink_slab+0x170/0x660
[ 1240.304601] shrink_node+0x7f7/0x1df0
[ 1240.305515] balance_pgdat+0x766/0xf50
[ 1240.306657] kswapd+0x5bd/0xd20
[ 1240.307551] kthread+0x34f/0x460
[ 1240.308346] ret_from_fork+0x22/0x30
[ 1240.309247]
[ 1240.309247] other info that might help us debug this:
[ 1240.309247]
[ 1240.310944] Possible unsafe locking scenario:
[ 1240.310944]
[ 1240.312379] CPU0 CPU1
[ 1240.313363] ---- ----
[ 1240.314433] lock(fs_reclaim);
[ 1240.315107] lock((work_completion)(&gc->work));
[ 1240.316828] lock(fs_reclaim);
[ 1240.318088] lock((work_completion)(&gc->work));
[ 1240.319203]
[ 1240.319203] *** DEADLOCK ***
...
[ 2438.431081] Workqueue: xfs-inodegc/sda xfs_inodegc_worker
[ 2438.432089] Call Trace:
[ 2438.432562] __schedule+0xa94/0x1d20
[ 2438.435787] schedule+0xbf/0x270
[ 2438.436397] schedule_timeout+0x6f8/0x8b0
[ 2438.445126] wait_for_completion+0x163/0x260
[ 2438.448610] __flush_work+0x4c4/0xa40
[ 2438.455011] xfs_inode_mark_reclaimable+0x6ef/0xda0
[ 2438.456695] destroy_inode+0xc6/0x1b0
[ 2438.457375] dispose_list+0xe1/0x1d0
[ 2438.458834] prune_icache_sb+0xe8/0x150
[ 2438.461181] super_cache_scan+0x2b3/0x470
[ 2438.461950] do_shrink_slab+0x3cf/0xa50
[ 2438.462687] shrink_slab+0x17d/0x660
[ 2438.466392] shrink_node+0x87e/0x1d40
[ 2438.467894] do_try_to_free_pages+0x364/0x1300
[ 2438.471188] try_to_free_pages+0x26c/0x5b0
[ 2438.473567] __alloc_pages_slowpath.constprop.136+0x7aa/0x2100
[ 2438.482577] __alloc_pages+0x5db/0x710
[ 2438.485231] alloc_pages+0x100/0x200
[ 2438.485923] allocate_slab+0x2c0/0x380
[ 2438.486623] ___slab_alloc+0x41f/0x690
[ 2438.490254] __slab_alloc+0x54/0x70
[ 2438.491692] kmem_cache_alloc+0x23e/0x270
[ 2438.492437] xfs_trans_alloc+0x88/0x880
[ 2438.493168] xfs_inactive_ifree+0xe2/0x4e0
[ 2438.496419] xfs_inactive+0x4eb/0x8b0
[ 2438.497123] xfs_inodegc_worker+0x16b/0x5e0
[ 2438.497918] process_one_work+0xbf7/0x1a20
[ 2438.500316] worker_thread+0x8c/0x1060
[ 2438.504938] ret_from_fork+0x22/0x30
When the memory is insufficient, xfs_inonodegc_worker will trigger memory
reclamation when memory is allocated, then flush_work() may be called to
wait for the work to complete. This causes a deadlock.
So if we need to wait for inodegc to complete, then we can handle that
instead of waiting for inodegc_worker to complete asynchronously.
Signed-off-by: Wu Guanghao <wuguanghao3@xxxxxxxxxx>
---
fs/xfs/xfs_icache.c | 25 ++++++++++++++++++-------
fs/xfs/xfs_trace.h | 2 +-
2 files changed, 19 insertions(+), 8 deletions(-)
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index f35e2cee5265..b7712a40caa2 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -1845,12 +1845,9 @@ xfs_inodegc_inactivate(
xfs_inodegc_set_reclaimable(ip);
}
-void
-xfs_inodegc_worker(
- struct work_struct *work)
+static void xfs_inodegc_process_inode(
+ struct xfs_inodegc *gc)
{
- struct xfs_inodegc *gc = container_of(to_delayed_work(work),
- struct xfs_inodegc, work);
struct llist_node *node = llist_del_all(&gc->list);
struct xfs_inode *ip, *n;
@@ -1860,7 +1857,7 @@ xfs_inodegc_worker(
return;
ip = llist_entry(node, struct xfs_inode, i_gclist);
- trace_xfs_inodegc_worker(ip->i_mount, READ_ONCE(gc->shrinker_hits));
+ trace_xfs_inodegc_process_inode(ip->i_mount, READ_ONCE(gc->shrinker_hits));
WRITE_ONCE(gc->shrinker_hits, 0);
llist_for_each_entry_safe(ip, n, node, i_gclist) {
@@ -1869,6 +1866,15 @@ xfs_inodegc_worker(
}
}
+void
+xfs_inodegc_worker(
+ struct work_struct *work)
+{
+ struct xfs_inodegc *gc = container_of(to_delayed_work(work),
+ struct xfs_inodegc, work);
+ xfs_inodegc_process_inode(gc);
+}
+
/*
* Expedite all pending inodegc work to run immediately. This does not wait for
* completion of the work.
@@ -2063,7 +2069,12 @@ xfs_inodegc_queue(
if (xfs_inodegc_want_flush_work(ip, items, shrinker_hits)) {
trace_xfs_inodegc_throttle(mp, __return_address);
- flush_delayed_work(&gc->work);
+ /*
+ * Can't use flush_delayed_work() to wait for work to complete,
+ * and a deadlock may occur when the memory shrinks. We need to
+ * be dealt with directly.
+ */
+ xfs_inodegc_process_inode(gc);
}
}
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 421d1e504ac4..3d5edbccdce7 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -192,7 +192,7 @@ DEFINE_PERAG_REF_EVENT(xfs_perag_put);
DEFINE_PERAG_REF_EVENT(xfs_perag_set_inode_tag);
DEFINE_PERAG_REF_EVENT(xfs_perag_clear_inode_tag);
-TRACE_EVENT(xfs_inodegc_worker,
+TRACE_EVENT(xfs_inodegc_process_inode,
TP_PROTO(struct xfs_mount *mp, unsigned int shrinker_hits),
TP_ARGS(mp, shrinker_hits),
TP_STRUCT__entry(
--
2.27.0
