Patch "lockd: drop inappropriate svc_get() from locked_get()" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    lockd: drop inappropriate svc_get() from locked_get()

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     lockd-drop-inappropriate-svc_get-from-locked_get.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5dacf787e8f831611210a80deb1d93464ed22107
Author: NeilBrown <neilb@xxxxxxx>
Date:   Sat Jun 3 07:14:14 2023 +1000

    lockd: drop inappropriate svc_get() from locked_get()
    
    [ Upstream commit 665e89ab7c5af1f2d260834c861a74b01a30f95f ]
    
    The below-mentioned patch was intended to simplify refcounting on the
    svc_serv used by locked.  The goal was to only ever have a single
    reference from the single thread.  To that end we dropped a call to
    lockd_start_svc() (except when creating thread) which would take a
    reference, and dropped the svc_put(serv) that would drop that reference.
    
    Unfortunately we didn't also remove the svc_get() from
    lockd_create_svc() in the case where the svc_serv already existed.
    So after the patch:
     - on the first call the svc_serv was allocated and the one reference
       was given to the thread, so there are no extra references
     - on subsequent calls svc_get() was called so there is now an extra
       reference.
    This is clearly not consistent.
    
    The inconsistency is also clear in the current code in lockd_get()
    takes *two* references, one on nlmsvc_serv and one by incrementing
    nlmsvc_users.   This clearly does not match lockd_put().
    
    So: drop that svc_get() from lockd_get() (which used to be in
    lockd_create_svc().
    
    Reported-by: Ido Schimmel <idosch@xxxxxxxxxx>
    Closes: https://lore.kernel.org/linux-nfs/ZHsI%2FH16VX9kJQX1@shredder/T/#u
    Fixes: b73a2972041b ("lockd: move lockd_start_svc() call into lockd_create_svc()")
    Signed-off-by: NeilBrown <neilb@xxxxxxx>
    Tested-by: Ido Schimmel <idosch@xxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 59ef8a1f843f3..5579e67da17db 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -355,7 +355,6 @@ static int lockd_get(void)
 	int error;
 
 	if (nlmsvc_serv) {
-		svc_get(nlmsvc_serv);
 		nlmsvc_users++;
 		return 0;
 	}