From: Greg Kroah-Hartman <gregkh@linuxfoundation•org>
To: Du Cheng <ducheng2@gmail•com>, Matthew Wilcox <willy@infradead•org>
Cc: "David S. Miller" <davem@davemloft•net>,
Jakub Kicinski <kuba@kernel•org>,
netdev@vger•kernel.org, Shuah Khan <skhan@linuxfoundation•org>,
syzbot+3eec59e770685e3dc879@syzkaller•appspotmail.com
Subject: Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()
Date: Sat, 27 Mar 2021 15:12:14 +0100 [thread overview]
Message-ID: <YF89PtWrs2N5XSgb@kroah.com> (raw)
In-Reply-To: <20210327140702.4916-1-ducheng2@gmail.com>
Adding the xarray maintainer...
On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> due to internal use of per_cpu variables, which requires preemption
> disabling/enabling.
>
> reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
>
> Reported-by: syzbot+3eec59e770685e3dc879@syzkaller•appspotmail.com
> Signed-off-by: Du Cheng <ducheng2@gmail•com>
> ---
> changelog
> v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> v2: revert to GFP_ATOMIC but add preemption disable/enable protection
>
> net/qrtr/qrtr.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> index edb6ac17ceca..6361f169490e 100644
> --- a/net/qrtr/qrtr.c
> +++ b/net/qrtr/qrtr.c
> @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> mutex_lock(&qrtr_port_lock);
> if (!*port) {
> min_port = QRTR_MIN_EPH_SOCKET;
> + idr_preload(GFP_ATOMIC);
> rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> + idr_preload_end();
This seems "odd" to me. We are asking idr_alloc_u32() to abide by
GFP_ATOMIC, so why do we need to "preload" it with the same type of
allocation?
Is there something in the idr/radix/xarray code that can't really handle
GFP_ATOMIC during a "normal" idr allocation that is causing this warning
to be hit? Why is this change the "correct" one?
thanks,
greg k-h
next prev parent reply other threads:[~2021-03-27 14:13 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-27 14:07 [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign() Du Cheng
2021-03-27 14:12 ` Greg Kroah-Hartman [this message]
2021-03-27 14:25 ` Du Cheng
2021-03-27 14:31 ` Greg Kroah-Hartman
2021-03-27 15:51 ` Matthew Wilcox
2021-03-28 6:56 ` Greg Kroah-Hartman
2021-03-28 10:04 ` Matthew Wilcox
2021-03-29 10:55 ` Du Cheng
2021-03-29 11:09 ` Manivannan Sadhasivam
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