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Message-ID: <Yz97YyDlV8tOr82t@codewreck.org>
Date: Fri, 7 Oct 2022 10:05:39 +0900
From: Dominique Martinet <asmadeus@...ewreck.org>
To: Christian Schoenebeck <linux_oss@...debyte.com>
Cc: v9fs-developer@...ts.sourceforge.net,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
syzbot <syzbot+2f20b523930c32c160cc@...kaller.appspotmail.com>,
syzkaller-bugs@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/9p: use a dedicated spinlock for trans_fd
Christian Schoenebeck wrote on Thu, Oct 06, 2022 at 03:16:40PM +0200:
> > net/9p/trans_fd.c | 42 ++++++++++++++++++++++++++----------------
> > 1 file changed, 26 insertions(+), 16 deletions(-)
>
> Late on the party, sorry. Note that you already queued a slightly different
> version than this patch here, anyway, one thing ...
Did I? Oh, I apparently reworded the commit message a bit, sorry:
(where HEAD is this patch and 1622... the queued patch)
$ git range-diff HEAD^- 16228c9a4215^-
1: e35fb8546af2 ! 1: 16228c9a4215 net/9p: use a dedicated spinlock for trans_fd
@@ Commit message
Since the locks actually protect different things in client.c and in
trans_fd.c, just replace trans_fd.c's lock by a new one specific to the
- transport instead of using spin_lock_irq* variants everywhere
- (client.c's protect the idr for tag allocations, while
- trans_fd.c's protects its own req list and request status field
+ transport (client.c's protect the idr for fid/tag allocations,
+ while trans_fd.c's protects its own req list and request status field
that acts as the transport's state machine)
- Link: https://lkml.kernel.org/r/20220904112928.1308799-1-asmadeus@codewreck.org
+ Link: https://lore.kernel.org/r/20220904112928.1308799-1-asmadeus@codewreck.org
Link: https://lkml.kernel.org/r/2470e028-9b05-2013-7198-1fdad071d999@I-love.SAKURA.ne.jp [1]
Link: https://syzkaller.appspot.com/bug?extid=2f20b523930c32c160cc [2]
Reported-by: syzbot <syzbot+2f20b523930c32c160cc@...kaller.appspotmail.com>
> > @@ -832,6 +840,7 @@ static int p9_fd_open(struct p9_client *client, int rfd,
> > int wfd)
> >
> > client->trans = ts;
> > client->status = Connected;
> > + spin_lock_init(&ts->conn.req_lock);
>
> Are you sure this is the right place for spin_lock_init()? Not rather in
> p9_conn_create()?
Good point, 'ts->conn' (named... m over there for some reason...) is
mostly initialized in p9_conn_create; it makes much more sense to move
it there despite being slightly further away from the allocation.
It's a bit of a pain to check as the code is spread over many paths (fd,
unix, tcp) but it looks equivalent to me:
- p9_fd_open is only called from p9_fd_create which immediately calls
p9_conn_create
- below p9_socket_open itself immediately calls p9_conn_create
I've moved the init and updated my next branch after very basic check
https://github.com/martinetd/linux/commit/e5cfd99e9ea6c13b3f0134585f269c509247ac0e:
----
diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 5b4807411281..d407f31bb49d 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -591,6 +591,7 @@ static void p9_conn_create(struct p9_client *client)
INIT_LIST_HEAD(&m->mux_list);
m->client = client;
+ spin_lock_init(&m->req_lock);
INIT_LIST_HEAD(&m->req_list);
INIT_LIST_HEAD(&m->unsent_req_list);
INIT_WORK(&m->rq, p9_read_work);
@@ -840,7 +841,6 @@ static int p9_fd_open(struct p9_client *client, int rfd, int wfd)
client->trans = ts;
client->status = Connected;
- spin_lock_init(&ts->conn.req_lock);
return 0;
@@ -875,7 +875,6 @@ static int p9_socket_open(struct p9_client *client, struct socket *csocket)
p->wr = p->rd = file;
client->trans = p;
client->status = Connected;
- spin_lock_init(&p->conn.req_lock);
p->rd->f_flags |= O_NONBLOCK;
----
> The rest LGTM.
Thank you for the look :)
--
Dominique
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