linux-kernel - Re: [PATCH] nvmet-fc: Fix a missed _irqsave version of spin_lock in 'nvmet_fc_fod_op

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Date:   Tue, 25 Aug 2020 09:09:40 +0200
From:   Christoph Hellwig <hch@....de>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Sagi Grimberg <sagi@...mberg.me>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        james.smart@...adcom.com, hch@....de, chaitanya.kulkarni@....com,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] nvmet-fc: Fix a missed _irqsave version of spin_lock
 in 'nvmet_fc_fod_op_done()'

On Mon, Aug 24, 2020 at 02:16:30PM -0700, Keith Busch wrote:
> On Mon, Aug 24, 2020 at 01:00:11PM -0700, Sagi Grimberg wrote:
> > > The way 'spin_lock()' and 'spin_lock_irqsave()' are used is not consistent
> > > in this function.
> > > 
> > > Use 'spin_lock_irqsave()' also here, as there is no guarantee that
> > > interruptions are disabled at that point, according to surrounding code.
> > > 
> > > Fixes: a97ec51b37ef ("nvmet_fc: Rework target side abort handling")
> > > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > > ---
> > > Not tested, only based on what looks logical to me according to
> > > surrounding code
> > > ---
> > >   drivers/nvme/target/fc.c | 4 ++--
> > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/nvme/target/fc.c b/drivers/nvme/target/fc.c
> > > index 55bafd56166a..e6861cc10e7d 100644
> > > --- a/drivers/nvme/target/fc.c
> > > +++ b/drivers/nvme/target/fc.c
> > > @@ -2342,9 +2342,9 @@ nvmet_fc_fod_op_done(struct nvmet_fc_fcp_iod *fod)
> > >   			return;
> > >   		if (fcpreq->fcp_error ||
> > >   		    fcpreq->transferred_length != fcpreq->transfer_length) {
> > > -			spin_lock(&fod->flock);
> > > +			spin_lock_irqsave(&fod->flock, flags);
> > >   			fod->abort = true;
> > > -			spin_unlock(&fod->flock);
> > > +			spin_unlock_irqrestore(&fod->flock, flags);
> > >   			nvmet_req_complete(&fod->req, NVME_SC_INTERNAL);
> > >   			return;
> > > 
> > 
> > James, can I get a reviewed-by from you on this?
> 
> afaics, the lock just serializes single writes, in which
> WRITE/READ_ONCE() can handle that without a lock, right?

It synchronizes a few fields, sometimes taken over multiple updates.