This patch fixes a race in async lock request handling between adding
the relevant struct nlm_block to nlm_blocked list after the request was
sent by vfs_lock_file() and nlmsvc_grant_deferred() does a lookup of the
nlm_block in the nlm_blocked list. It could be that the async request is
completed before the nlm_block was added to the list. This would end
in a -ENOENT and a kernel log message of "lockd: grant for unknown
block".
To solve this issue we add the nlm_block before the vfs_lock_file() call
to be sure it has been added when a possible nlmsvc_grant_deferred() is
called. If the vfs_lock_file() results in an case when it wouldn't be
added to nlm_blocked list, the nlm_block struct will be removed from
this list again.
The introducing of the new B_PENDING_CALLBACK nlm_block flag will handle
async lock requests on a pending lock requests as a retry on the caller
level to hit the -EAGAIN case.
Signed-off-by: Alexander Aring <aahringo@xxxxxxxxxx>
---
fs/lockd/svclock.c | 100 ++++++++++++++++++++++++++----------
include/linux/lockd/lockd.h | 2 +
2 files changed, 74 insertions(+), 28 deletions(-)
diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index c43ccdf28ed9..7d63524bdb81 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -133,6 +133,7 @@ nlmsvc_remove_block(struct nlm_block *block)
{
if (!list_empty(&block->b_list)) {
spin_lock(&nlm_blocked_lock);
+ block->b_flags &= ~B_PENDING_CALLBACK;
list_del_init(&block->b_list);
spin_unlock(&nlm_blocked_lock);
nlmsvc_release_block(block);
@@ -232,6 +233,7 @@ nlmsvc_create_block(struct svc_rqst *rqstp, struct nlm_host *host,
kref_init(&block->b_count);
INIT_LIST_HEAD(&block->b_list);
INIT_LIST_HEAD(&block->b_flist);
+ mutex_init(&block->b_cb_mutex);
if (!nlmsvc_setgrantargs(call, lock))
goto failed_free;
@@ -289,6 +291,8 @@ static void nlmsvc_free_block(struct kref *kref)
dprintk("lockd: freeing block %p...\n", block);
+ WARN_ON_ONCE(block->b_flags & B_PENDING_CALLBACK);
+
/* Remove block from file's list of blocks */
list_del_init(&block->b_flist);
mutex_unlock(&file->f_mutex);
@@ -532,6 +536,13 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
goto out;
}
+ mutex_lock(&block->b_cb_mutex);
+ if (block->b_flags & B_PENDING_CALLBACK)
+ goto pending_request;
+
+ /* Append to list of blocked */
+ nlmsvc_insert_block(block, NLM_NEVER);
+
if (!wait)
lock->fl.fl_flags &= ~FL_SLEEP;
mode = lock_to_openmode(&lock->fl);
@@ -541,9 +552,13 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
dprintk("lockd: vfs_lock_file returned %d\n", error);
switch (error) {
case 0:
+ nlmsvc_remove_block(block);
ret = nlm_granted;
- goto out;
+ goto out_cb_mutex;
case -EAGAIN:
+ if (!wait)
+ nlmsvc_remove_block(block);
+pending_request:
/*
* If this is a blocking request for an
* already pending lock request then we need
@@ -552,26 +567,29 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
if (wait)
break;
ret = async_block ? nlm_lck_blocked : nlm_lck_denied;
- goto out;
+ goto out_cb_mutex;
case FILE_LOCK_DEFERRED:
+ block->b_flags |= B_PENDING_CALLBACK;
+
if (wait)
break;
/* Filesystem lock operation is in progress
Add it to the queue waiting for callback */
ret = nlmsvc_defer_lock_rqst(rqstp, block);
- goto out;
+ goto out_cb_mutex;
case -EDEADLK:
+ nlmsvc_remove_block(block);
ret = nlm_deadlock;
- goto out;
+ goto out_cb_mutex;
default: /* includes ENOLCK */
+ nlmsvc_remove_block(block);
ret = nlm_lck_denied_nolocks;
- goto out;
+ goto out_cb_mutex;
}
ret = nlm_lck_blocked;
-
- /* Append to list of blocked */
- nlmsvc_insert_block(block, NLM_NEVER);
+out_cb_mutex:
+ mutex_unlock(&block->b_cb_mutex);
out:
mutex_unlock(&file->f_mutex);
nlmsvc_release_block(block);
@@ -728,34 +746,60 @@ nlmsvc_update_deferred_block(struct nlm_block *block, int result)
block->b_flags |= B_TIMED_OUT;
}
+static int __nlmsvc_grant_deferred(struct nlm_block *block,
+ struct file_lock *fl,
+ int result)
+{
+ int rc = 0;
+
+ dprintk("lockd: nlmsvc_notify_blocked block %p flags %d\n",
+ block, block->b_flags);
+ if (block->b_flags & B_QUEUED) {
+ if (block->b_flags & B_TIMED_OUT) {
+ rc = -ENOLCK;
+ goto out;
+ }
+ nlmsvc_update_deferred_block(block, result);
+ } else if (result == 0)
+ block->b_granted = 1;
+
+ nlmsvc_insert_block_locked(block, 0);
+ svc_wake_up(block->b_daemon);
+out:
+ return rc;
+}
+
static int nlmsvc_grant_deferred(struct file_lock *fl, int result)
{
- struct nlm_block *block;
- int rc = -ENOENT;
+ struct nlm_block *iter, *block = NULL;
+ int rc;
spin_lock(&nlm_blocked_lock);
- list_for_each_entry(block, &nlm_blocked, b_list) {
- if (nlm_compare_locks(&block->b_call->a_args.lock.fl, fl)) {
- dprintk("lockd: nlmsvc_notify_blocked block %p flags %d\n",
- block, block->b_flags);
- if (block->b_flags & B_QUEUED) {
- if (block->b_flags & B_TIMED_OUT) {
- rc = -ENOLCK;
- break;
- }
- nlmsvc_update_deferred_block(block, result);
- } else if (result == 0)
- block->b_granted = 1;
-
- nlmsvc_insert_block_locked(block, 0);
- svc_wake_up(block->b_daemon);
- rc = 0;
+ list_for_each_entry(iter, &nlm_blocked, b_list) {
+ if (nlm_compare_locks(&iter->b_call->a_args.lock.fl, fl)) {
+ kref_get(&iter->b_count);
+ block = iter;
break;
}
}
spin_unlock(&nlm_blocked_lock);
- if (rc == -ENOENT)
- printk(KERN_WARNING "lockd: grant for unknown block\n");
+
+ if (!block) {
+ pr_warn("lockd: grant for unknown pending block\n");
+ return -ENOENT;
+ }
+
+ /* don't interfere with nlmsvc_lock() */
+ mutex_lock(&block->b_cb_mutex);
+ block->b_flags &= ~B_PENDING_CALLBACK;
+
+ spin_lock(&nlm_blocked_lock);
+ WARN_ON_ONCE(list_empty(&block->b_list));
+ rc = __nlmsvc_grant_deferred(block, fl, result);
+ spin_unlock(&nlm_blocked_lock);
+ mutex_unlock(&block->b_cb_mutex);
+
+ nlmsvc_release_block(block);
return rc;
}
diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index f42594a9efe0..91f55458f5fc 100644
--- a/include/linux/lockd/lockd.h
+++ b/include/linux/lockd/lockd.h
@@ -185,10 +185,12 @@ struct nlm_block {
struct nlm_file * b_file; /* file in question */
struct cache_req * b_cache_req; /* deferred request handling */
struct cache_deferred_req * b_deferred_req;
+ struct mutex b_cb_mutex; /* callback mutex */
unsigned int b_flags; /* block flags */
#define B_QUEUED 1 /* lock queued */
#define B_GOT_CALLBACK 2 /* got lock or conflicting lock */
#define B_TIMED_OUT 4 /* filesystem too slow to respond */
+#define B_PENDING_CALLBACK 8 /* pending callback for lock request */
};
/*
--
2.31.1
