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fs: dlm: fix race in nodeid2con

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This patch fixes a race in nodeid2con in cases that we parallel running
a lookup and both will create a connection structure for the same nodeid.
It's a rare case to create a new connection structure to keep reader
lockless we just do a lookup inside the protection area again and drop
previous work if this race happens.

Fixes: a47666eb76 ("fs: dlm: make connection hash lockless")
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>
This commit is contained in:
Alexander Aring 2020-09-30 18:37:29 -04:00 committed by David Teigland
parent 4798cbbfbd
commit 4f2b30fd9b
1 changed files with 15 additions and 1 deletions
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16
fs/dlm/lowcomms.c
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@ -175,7 +175,7 @@ static struct connection *__find_con(int nodeid)
*/
static struct connection *nodeid2con(int nodeid, gfp_t alloc)
{
struct connection *con = NULL;
struct connection *con, *tmp;
int r;
con = __find_con(nodeid);
@ -213,6 +213,20 @@ static struct connection *nodeid2con(int nodeid, gfp_t alloc)
r = nodeid_hash(nodeid);
spin_lock(&connections_lock);
/* Because multiple workqueues/threads calls this function it can
* race on multiple cpu's. Instead of locking hot path __find_con()
* we just check in rare cases of recently added nodes again
* under protection of connections_lock. If this is the case we
* abort our connection creation and return the existing connection.
*/
tmp = __find_con(nodeid);
if (tmp) {
spin_unlock(&connections_lock);
kfree(con->rx_buf);
kfree(con);
return tmp;
}
hlist_add_head_rcu(&con->list, &connection_hash[r]);
spin_unlock(&connections_lock);