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Use seqlock instead of seqcount in server

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The server had a few lower level seqcounts that it used to protect
state.  One user got it wrong by forgetting to disable pre-emption
around writers.  Debug kernels warned as write_seqcount_begin() was
called without preemption disabled.

We fix that user and make it easier to get right in the future by having
one higher level seqlock and using that consistently for seq read
begin/retry and write lock/unlock patterns.

Signed-off-by: Zach Brown <zab@versity.com>
This commit is contained in:
Zach Brown
2023-10-19 15:37:19 -07:00
parent 9f06065ce7
commit 006f429f72
1 changed files with 16 additions and 20 deletions
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36
kmod/src/server.c
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@@ -91,6 +91,7 @@ do { \
struct server_info {
struct super_block *sb;
spinlock_t lock;
seqlock_t seqlock;
wait_queue_head_t waitq;
struct workqueue_struct *wq;
@@ -132,11 +133,9 @@ struct server_info {
struct mutex mounted_clients_mutex;
/* stable super stored from commits, given in locks and rpcs */
seqcount_t stable_seqcount;
struct scoutfs_super_block stable_super;
/* serializing and get and set volume options */
seqcount_t volopt_seqcount;
struct mutex volopt_mutex;
struct scoutfs_volume_options volopt;
@@ -182,7 +181,7 @@ static bool get_volopt_val(struct server_info *server, int nr, u64 *val)
unsigned seq;
do {
seq = read_seqcount_begin(&server->volopt_seqcount);
seq = read_seqbegin(&server->seqlock);
if ((le64_to_cpu(server->volopt.set_bits) & bit)) {
is_set = true;
*val = le64_to_cpup(opt);
@@ -190,7 +189,7 @@ static bool get_volopt_val(struct server_info *server, int nr, u64 *val)
is_set = false;
*val = 0;
};
} while (read_seqcount_retry(&server->volopt_seqcount, seq));
} while (read_seqretry(&server->seqlock, seq));
return is_set;
}
@@ -506,7 +505,7 @@ static void get_stable(struct super_block *sb, struct scoutfs_super_block *super
unsigned int seq;
do {
seq = read_seqcount_begin(&server->stable_seqcount);
seq = read_seqbegin(&server->seqlock);
if (super)
*super = server->stable_super;
if (roots) {
@@ -514,7 +513,7 @@ static void get_stable(struct super_block *sb, struct scoutfs_super_block *super
roots->logs_root = server->stable_super.logs_root;
roots->srch_root = server->stable_super.srch_root;
}
} while (read_seqcount_retry(&server->stable_seqcount, seq));
} while (read_seqretry(&server->seqlock, seq));
}
u64 scoutfs_server_seq(struct super_block *sb)
@@ -548,11 +547,9 @@ void scoutfs_server_set_seq_if_greater(struct super_block *sb, u64 seq)
static void set_stable_super(struct server_info *server, struct scoutfs_super_block *super)
{
preempt_disable();
write_seqcount_begin(&server->stable_seqcount);
write_seqlock(&server->seqlock);
server->stable_super = *super;
write_seqcount_end(&server->stable_seqcount);
preempt_enable();
write_sequnlock(&server->seqlock);
}
/*
@@ -3073,9 +3070,9 @@ static int server_get_volopt(struct super_block *sb, struct scoutfs_net_connecti
}
do {
seq = read_seqcount_begin(&server->volopt_seqcount);
seq = read_seqbegin(&server->seqlock);
volopt = server->volopt;
} while (read_seqcount_retry(&server->volopt_seqcount, seq));
} while (read_seqretry(&server->seqlock, seq));
out:
return scoutfs_net_response(sb, conn, cmd, id, ret, &volopt, sizeof(volopt));
@@ -3144,12 +3141,12 @@ static int server_set_volopt(struct super_block *sb, struct scoutfs_net_connecti
apply:
ret = server_apply_commit(sb, &hold, ret);
write_seqcount_begin(&server->volopt_seqcount);
write_seqlock(&server->seqlock);
if (ret == 0)
server->volopt = super->volopt;
else
super->volopt = server->volopt;
write_seqcount_end(&server->volopt_seqcount);
write_sequnlock(&server->seqlock);
mutex_unlock(&server->volopt_mutex);
out:
@@ -3192,12 +3189,12 @@ static int server_clear_volopt(struct super_block *sb, struct scoutfs_net_connec
ret = server_apply_commit(sb, &hold, ret);
write_seqcount_begin(&server->volopt_seqcount);
write_seqlock(&server->seqlock);
if (ret == 0)
server->volopt = super->volopt;
else
super->volopt = server->volopt;
write_seqcount_end(&server->volopt_seqcount);
write_sequnlock(&server->seqlock);
mutex_unlock(&server->volopt_mutex);
out:
@@ -4336,9 +4333,9 @@ static void scoutfs_server_worker(struct work_struct *work)
}
/* update volume options early, possibly for use during startup */
write_seqcount_begin(&server->volopt_seqcount);
write_seqlock(&server->seqlock);
server->volopt = super->volopt;
write_seqcount_end(&server->volopt_seqcount);
write_sequnlock(&server->seqlock);
atomic64_set(&server->seq_atomic, le64_to_cpu(super->seq));
set_stable_super(server, super);
@@ -4478,6 +4475,7 @@ int scoutfs_server_setup(struct super_block *sb)
server->sb = sb;
spin_lock_init(&server->lock);
seqlock_init(&server->seqlock);
init_waitqueue_head(&server->waitq);
INIT_WORK(&server->work, scoutfs_server_worker);
server->status = SERVER_DOWN;
@@ -4492,8 +4490,6 @@ int scoutfs_server_setup(struct super_block *sb)
INIT_WORK(&server->log_merge_free_work, server_log_merge_free_work);
mutex_init(&server->srch_mutex);
mutex_init(&server->mounted_clients_mutex);
seqcount_init(&server->stable_seqcount);
seqcount_init(&server->volopt_seqcount);
mutex_init(&server->volopt_mutex);
INIT_WORK(&server->fence_pending_recov_work, fence_pending_recov_worker);
INIT_DELAYED_WORK(&server->reclaim_dwork, reclaim_worker);