linux-kernel - Re: [PATCH 1/2] mpt2sas: Refcount sas_device objects and fix unsafe list usage

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Message-ID: <20150721070620.GB1353000@mail.thefacebook.com>
Date:	Tue, 21 Jul 2015 00:06:20 -0700
From:	Calvin Owens <calvinowens@...com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	<MPT-FusionLinux.pdl@...gotech.com>, <linux-scsi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <kernel-team@...com>,
	Bart Van Assche <bart.vanassche@...disk.com>
Subject: Re: [PATCH 1/2] mpt2sas: Refcount sas_device objects and fix unsafe
 list usage

On Sunday 07/12 at 23:52 -0700, Christoph Hellwig wrote:
> On Sat, Jul 11, 2015 at 09:24:55PM -0700, Calvin Owens wrote:
> > These objects can be referenced concurrently throughout the driver, we
> > need a way to make sure threads can't delete them out from under each
> > other. This patch adds the refcount, and refactors the code to use it.
> > 
> > Additionally, we cannot iterate over the sas_device_list without
> > holding the lock, or we risk corrupting random memory if items are
> > added or deleted as we iterate. This patch refactors _scsih_probe_sas()
> > to use the sas_device_list in a safe way.
> > 
> > Cc: Christoph Hellwig <hch@...radead.org>
> > Cc: Bart Van Assche <bart.vanassche@...disk.com>
> > Signed-off-by: Calvin Owens <calvinowens@...com>
> > ---
> >  drivers/scsi/mpt2sas/mpt2sas_base.h      |  22 +-
> >  drivers/scsi/mpt2sas/mpt2sas_scsih.c     | 434 ++++++++++++++++++++-----------
> >  drivers/scsi/mpt2sas/mpt2sas_transport.c |  12 +-
> >  3 files changed, 315 insertions(+), 153 deletions(-)
> > 
> > diff --git a/drivers/scsi/mpt2sas/mpt2sas_base.h b/drivers/scsi/mpt2sas/mpt2sas_base.h
> > index caff8d1..78f41ac 100644
> > --- a/drivers/scsi/mpt2sas/mpt2sas_base.h
> > +++ b/drivers/scsi/mpt2sas/mpt2sas_base.h
> > @@ -238,6 +238,7 @@
> >   * @flags: MPT_TARGET_FLAGS_XXX flags
> >   * @deleted: target flaged for deletion
> >   * @tm_busy: target is busy with TM request.
> > + * @sdev: The sas_device associated with this target
> >   */
> >  struct MPT2SAS_TARGET {
> >  	struct scsi_target *starget;
> > @@ -248,6 +249,7 @@ struct MPT2SAS_TARGET {
> >  	u32	flags;
> >  	u8	deleted;
> >  	u8	tm_busy;
> > +	struct _sas_device *sdev;
> >  };
> >  
> >  
> > @@ -376,8 +378,24 @@ struct _sas_device {
> >  	u8	phy;
> >  	u8	responding;
> >  	u8	pfa_led_on;
> > +	struct kref refcount;
> >  };
> >  
> > +static inline void sas_device_get(struct _sas_device *s)
> > +{
> > +	kref_get(&s->refcount);
> > +}
> > +
> > +static inline void sas_device_free(struct kref *r)
> > +{
> > +	kfree(container_of(r, struct _sas_device, refcount));
> > +}
> > +
> > +static inline void sas_device_put(struct _sas_device *s)
> > +{
> > +	kref_put(&s->refcount, sas_device_free);
> > +}
> > +
> >  /**
> >   * struct _raid_device - raid volume link list
> >   * @list: sas device list
> > @@ -1095,7 +1113,9 @@ struct _sas_node *mpt2sas_scsih_expander_find_by_handle(struct MPT2SAS_ADAPTER *
> >      u16 handle);
> >  struct _sas_node *mpt2sas_scsih_expander_find_by_sas_address(struct MPT2SAS_ADAPTER
> >      *ioc, u64 sas_address);
> > -struct _sas_device *mpt2sas_scsih_sas_device_find_by_sas_address(
> > +struct _sas_device *mpt2sas_get_sdev_by_addr(
> > +    struct MPT2SAS_ADAPTER *ioc, u64 sas_address);
> > +struct _sas_device *__mpt2sas_get_sdev_by_addr(
> >      struct MPT2SAS_ADAPTER *ioc, u64 sas_address);
> >  
> >  void mpt2sas_port_enable_complete(struct MPT2SAS_ADAPTER *ioc);
> > diff --git a/drivers/scsi/mpt2sas/mpt2sas_scsih.c b/drivers/scsi/mpt2sas/mpt2sas_scsih.c
> > index 3f26147..fad80ce 100644
> > --- a/drivers/scsi/mpt2sas/mpt2sas_scsih.c
> > +++ b/drivers/scsi/mpt2sas/mpt2sas_scsih.c
> > @@ -526,8 +526,43 @@ _scsih_determine_boot_device(struct MPT2SAS_ADAPTER *ioc,
> >  	}
> >  }
> >  
> > +struct _sas_device *
> > +__mpt2sas_get_sdev_from_target(struct MPT2SAS_TARGET *tgt_priv)
> > +{
> > +	struct _sas_device *ret;
> > +
> 
> Does this need a:
> 
> 	assert_spin_locked(&ioc->sas_device_lock);
> 
> ?

Yeah: I'll add that.

Thanks very much,
Calvin

> Otherwise this looks sensible to me.
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