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Date: Wed, 22 Jan 2020 10:45:39 +0800 From: "sunke (E)" <sunke32@...wei.com> To: Jens Axboe <axboe@...nel.dk>, Josef Bacik <josef@...icpanda.com>, <mchristi@...hat.com> CC: <linux-block@...r.kernel.org>, <nbd@...er.debian.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] nbd: add a flush_workqueue in nbd_start_device 在 2020/1/22 5:25, Jens Axboe 写道: > On 1/21/20 7:00 AM, Josef Bacik wrote: >> On 1/21/20 7:48 AM, Sun Ke wrote: >>> When kzalloc fail, may cause trying to destroy the >>> workqueue from inside the workqueue. >>> >>> If num_connections is m (2 < m), and NO.1 ~ NO.n >>> (1 < n < m) kzalloc are successful. The NO.(n + 1) >>> failed. Then, nbd_start_device will return ENOMEM >>> to nbd_start_device_ioctl, and nbd_start_device_ioctl >>> will return immediately without running flush_workqueue. >>> However, we still have n recv threads. If nbd_release >>> run first, recv threads may have to drop the last >>> config_refs and try to destroy the workqueue from >>> inside the workqueue. >>> >>> To fix it, add a flush_workqueue in nbd_start_device. >>> >>> Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs") >>> Signed-off-by: Sun Ke <sunke32@...wei.com> >>> --- >>> drivers/block/nbd.c | 7 ++++++- >>> 1 file changed, 6 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c >>> index b4607dd96185..dd1f8c2c6169 100644 >>> --- a/drivers/block/nbd.c >>> +++ b/drivers/block/nbd.c >>> @@ -1264,7 +1264,12 @@ static int nbd_start_device(struct nbd_device *nbd) >>> >>> args = kzalloc(sizeof(*args), GFP_KERNEL); >>> if (!args) { >>> - sock_shutdown(nbd); >>> + if (i == 0) >>> + sock_shutdown(nbd); >>> + else { >>> + sock_shutdown(nbd); >>> + flush_workqueue(nbd->recv_workq); >>> + } >> >> Just for readability sake why don't we just flush_workqueue() >> unconditionally, and add a comment so we know why in the future. > > Or maybe just make it: > > sock_shutdown(nbd); > if (i) > flush_workqueue(nbd->recv_workq); > > which does the same thing, but is still readable. The current code with > the shutdown duplication is just a bit odd. Needs a comment either way. > OK, I will improve it in my v2 patch. Thanks, Sun Ke
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