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Consistently lock server mounted_clients btree

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The mounted_clients btree stores items to track mounted clients.  It's
modified by multiple greeting workers and the farewell work.

The greeting work was serialized by the farewell_mutex, but the
modifications in the farewell thread weren't protected.  This could
result in modifications between the threads being lost if the dirty
block reference updates raced in just the right way.  I saw this in
testing with deletions in farewell being lost and then that lingering
item preventing unmount because the server thought it had to wait for a
remaining quorum member to unmount.

We fix this by adding a mutex specifically to protect the
mounted_clients btree in the server.

Signed-off-by: Zach Brown <zab@versity.com>
This commit is contained in:
Zach Brown
2021-02-05 11:29:15 -08:00
parent 57f34e90e9
commit d53350f9f1
1 changed files with 16 additions and 5 deletions
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21
kmod/src/server.c
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@@ -91,6 +91,7 @@ struct server_info {
struct mutex logs_mutex;
struct mutex srch_mutex;
struct mutex mounted_clients_mutex;
/* stable versions stored from commits, given in locks and rpcs */
seqcount_t roots_seqcount;
@@ -1030,15 +1031,20 @@ static int insert_mounted_client(struct super_block *sb, u64 rid,
struct scoutfs_super_block *super = &SCOUTFS_SB(sb)->super;
struct scoutfs_mounted_client_btree_val mcv;
struct scoutfs_key key;
int ret;
init_mounted_client_key(&key, rid);
mcv.flags = 0;
if (gr_flags & SCOUTFS_NET_GREETING_FLAG_QUORUM)
mcv.flags |= SCOUTFS_MOUNTED_CLIENT_QUORUM;
return scoutfs_btree_insert(sb, &server->alloc, &server->wri,
&super->mounted_clients, &key, &mcv,
sizeof(mcv));
mutex_lock(&server->mounted_clients_mutex);
ret = scoutfs_btree_insert(sb, &server->alloc, &server->wri,
&super->mounted_clients, &key, &mcv,
sizeof(mcv));
mutex_unlock(&server->mounted_clients_mutex);
return ret;
}
/*
@@ -1057,8 +1063,10 @@ static int delete_mounted_client(struct super_block *sb, u64 rid)
init_mounted_client_key(&key, rid);
mutex_lock(&server->mounted_clients_mutex);
ret = scoutfs_btree_delete(sb, &server->alloc, &server->wri,
&super->mounted_clients, &key);
mutex_unlock(&server->mounted_clients_mutex);
if (ret == -ENOENT)
ret = 0;
@@ -1177,10 +1185,8 @@ static int server_greeting(struct super_block *sb,
if (ret < 0)
goto send_err;
mutex_lock(&server->farewell_mutex);
ret = insert_mounted_client(sb, le64_to_cpu(gr->rid),
le64_to_cpu(gr->flags));
mutex_unlock(&server->farewell_mutex);
ret = scoutfs_server_apply_commit(sb, ret);
queue_work(server->wq, &server->farewell_work);
@@ -1297,8 +1303,10 @@ static void farewell_worker(struct work_struct *work)
nr_unmounting = 0;
list_for_each_entry_safe(fw, tmp, &reqs, entry) {
init_mounted_client_key(&key, fw->rid);
mutex_lock(&server->mounted_clients_mutex);
ret = scoutfs_btree_lookup(sb, &super->mounted_clients, &key,
&iref);
mutex_unlock(&server->mounted_clients_mutex);
if (ret == 0 && invalid_mounted_client_item(&iref)) {
scoutfs_btree_put_iref(&iref);
ret = -EIO;
@@ -1326,8 +1334,10 @@ static void farewell_worker(struct work_struct *work)
/* see how many mounted clients are quorum members */
init_mounted_client_key(&key, 0);
for (;;) {
mutex_lock(&server->mounted_clients_mutex);
ret = scoutfs_btree_next(sb, &super->mounted_clients, &key,
&iref);
mutex_unlock(&server->mounted_clients_mutex);
if (ret == 0 && invalid_mounted_client_item(&iref)) {
scoutfs_btree_put_iref(&iref);
ret = -EIO;
@@ -1696,6 +1706,7 @@ int scoutfs_server_setup(struct super_block *sb)
mutex_init(&server->alloc_mutex);
mutex_init(&server->logs_mutex);
mutex_init(&server->srch_mutex);
mutex_init(&server->mounted_clients_mutex);
seqcount_init(&server->roots_seqcount);
server->wq = alloc_workqueue("scoutfs_server",