On 9/2/22 10:58 AM, Chuck Lever III wrote:
Or, nfsd_courtesy_client_count() could return
nfsd_couresy_client_count. nfsd_courtesy_client_scan() could
then look something like this:
if ((sc->gfp_mask & GFP_KERNEL) != GFP_KERNEL)
return SHRINK_STOP;
nfsd_get_client_reaplist(nn, reaplist, lt);
list_for_each_safe(pos, next, &reaplist) {
clp = list_entry(pos, struct nfs4_client, cl_lru);
trace_nfsd_clid_purged(&clp->cl_clientid);
list_del_init(&clp->cl_lru);
expire_client(clp);
count++;
}
return count;
This does not work, we cannot expire clients on the context of
scan callback due to deadlock problem.
Correct, we don't want to start shrinker laundromat activity if
the allocation request specified that it cannot wait. But are
you sure it doesn't work if sc_gfp_flags is set to GFP_KERNEL?
It can be deadlock due to lock ordering problem:
======================================================
WARNING: possible circular locking dependency detected
5.19.0-rc2_sk+ #1 Not tainted
------------------------------------------------------
lck/31847 is trying to acquire lock:
ffff88811d268850 (&sb->s_type->i_mutex_key#16){+.+.}-{3:3}, at: btrfs_inode_lock+0x38/0x70
#012but task is already holding lock:
ffffffffb41848c0 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0x506/0x1db0
#012which lock already depends on the new lock.
#012the existing dependency chain (in reverse order) is:
#012-> #1 (fs_reclaim){+.+.}-{0:0}:
fs_reclaim_acquire+0xc0/0x100
__kmalloc+0x51/0x320
btrfs_buffered_write+0x2eb/0xd90
btrfs_do_write_iter+0x6bf/0x11c0
do_iter_readv_writev+0x2bb/0x5a0
do_iter_write+0x131/0x630
nfsd_vfs_write+0x4da/0x1900 [nfsd]
nfsd4_write+0x2ac/0x760 [nfsd]
nfsd4_proc_compound+0xce8/0x23e0 [nfsd]
nfsd_dispatch+0x4ed/0xc10 [nfsd]
svc_process_common+0xd3f/0x1b00 [sunrpc]
svc_process+0x361/0x4f0 [sunrpc]
nfsd+0x2d6/0x570 [nfsd]
kthread+0x2a1/0x340
ret_from_fork+0x22/0x30
#012-> #0 (&sb->s_type->i_mutex_key#16){+.+.}-{3:3}:
__lock_acquire+0x318d/0x7830
lock_acquire+0x1bb/0x500
down_write+0x82/0x130
btrfs_inode_lock+0x38/0x70
btrfs_sync_file+0x280/0x1010
nfsd_file_flush.isra.0+0x1b/0x220 [nfsd]
nfsd_file_put+0xd4/0x110 [nfsd]
release_all_access+0x13a/0x220 [nfsd]
nfs4_free_ol_stateid+0x40/0x90 [nfsd]
free_ol_stateid_reaplist+0x131/0x210 [nfsd]
release_openowner+0xf7/0x160 [nfsd]
__destroy_client+0x3cc/0x740 [nfsd]
nfsd_cc_lru_scan+0x271/0x410 [nfsd]
shrink_slab.constprop.0+0x31e/0x7d0
shrink_node+0x54b/0xe50
try_to_free_pages+0x394/0xba0
__alloc_pages_slowpath.constprop.0+0x5d2/0x1db0
__alloc_pages+0x4d6/0x580
__handle_mm_fault+0xc25/0x2810
handle_mm_fault+0x136/0x480
do_user_addr_fault+0x3d8/0xec0
exc_page_fault+0x5d/0xc0
asm_exc_page_fault+0x27/0x30
-Dai
