From: Jason Gunthorpe <jgg@mellanox.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>
Subject: Re: [PATCH] RDMA/ucma: Put a lock around every call to the rdma_cm layer
Date: Wed, 19 Feb 2020 20:22:25 +0000 [thread overview]
Message-ID: <20200219202221.GN23930@mellanox.com> (raw)
In-Reply-To: <20200219060701.GG1075@sol.localdomain>
On Tue, Feb 18, 2020 at 10:07:01PM -0800, Eric Biggers wrote:
> > these 11 lets include them as well. I wasn't able to find a way to
> > search for things, this list is from your past email, thanks.
> >
>
> Unfortunately I haven't had time to work on syzkaller bugs lately, so I can't
> provide an updated list until I go through the long backlog of bugs.
Ok
> A comment on the patch below:
>
> > @@ -1112,13 +1134,17 @@ static ssize_t ucma_accept(struct ucma_file *file, const char __user *inbuf,
> > if (cmd.conn_param.valid) {
> > ucma_copy_conn_param(ctx->cm_id, &conn_param, &cmd.conn_param);
> > mutex_lock(&file->mut);
> > + mutex_lock(&ctx->mutex);
> > ret = __rdma_accept(ctx->cm_id, &conn_param, NULL);
> > + mutex_unlock(&ctx->mutex);
> > if (!ret)
> > ctx->uid = cmd.uid;
> > mutex_unlock(&file->mut);
>
> This is nesting the new ucma_context::mutex inside the existing ucma_file::mut.
Ah, indeed
> > @@ -1403,6 +1443,7 @@ static ssize_t ucma_process_join(struct ucma_file *file,
> > if (IS_ERR(ctx))
> > return PTR_ERR(ctx);
> >
> > + mutex_lock(&ctx->mutex);
> > mutex_lock(&file->mut);
> > mc = ucma_alloc_multicast(ctx);
> > if (!mc) {
>
> ... but this is doing the opposite. So it can deadlock.
Lets narrow this one to just rdma_join_multicast(), looks safe
> What's the intended order?
The code works better if mut is the exterior lock, it seems
> Also, are these two separate mutexes actually needed? I.e., did you consider
> using the existing ucma_file::mut, but it didn't work or it wasn't fine-grained
> enough? (It looks like one ucma_file can have multiple ucma_contexts.)
It would probably work, but it is not as fine grained as a per-ctx
lock, and some people do care about performance with this stuff.
The file->mut is protecting some global per-fd lists it seems.
Thanks,
Jason
next prev parent reply other threads:[~2020-02-19 20:22 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-18 21:04 [PATCH] RDMA/ucma: Put a lock around every call to the rdma_cm layer Jason Gunthorpe
2020-02-18 22:10 ` KASAN: use-after-free Read in rdma_listen (2) syzbot
2020-02-19 6:07 ` [PATCH] RDMA/ucma: Put a lock around every call to the rdma_cm layer Eric Biggers
2020-02-19 20:22 ` Jason Gunthorpe [this message]
2020-03-07 20:41 ` Eric Biggers
2020-03-09 19:30 ` Jason Gunthorpe
2020-06-27 22:57 ` Eric Biggers
2020-06-29 14:30 ` Jason Gunthorpe
2020-11-16 20:46 ` Jason Gunthorpe
2020-02-27 20:42 ` Jason Gunthorpe
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