From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH] fix NULL-pointer dereference on scsi_run_queue Date: Mon, 06 Aug 2012 17:56:49 +0000 Message-ID: <50200561.4020100@acm.org> References: <501CE4E5.20604@acm.org> <501D51D1.2010806@cs.wisc.edu> <501D83A1.7040900@acm.org> <501DA3F0.4090009@cs.wisc.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <501DA3F0.4090009@cs.wisc.edu> Sender: linux-kernel-owner@vger.kernel.org To: Mike Christie Cc: Chanho Min , James Bottomley , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe , Tejun Heo List-Id: linux-scsi@vger.kernel.org On 08/04/12 22:36, Mike Christie wrote: > On 08/04/2012 03:18 PM, Bart Van Assche wrote: >> On 08/04/12 16:46, Mike Christie wrote: >>> I think we have to have scsi-ml do a get_device when a sdev is added to >>> the starved entry and then do a put_device when it is removed (must do >>> these under the host lock for the starved entry case too). I am not sure >>> if that is just a hack/papering-over of the problem and there are more >>> issues like this. >> >> That would result in a more complex patch than the patch at the start of >> this thread, isn't it ? > > Yaah, but the original patch in this thread is still racey isn't it? Indeed. How about the patch below ? Scsi devices are removed from starved_list after blk_cleanup_queue() and before put_device(). That guarantees that inside scsi_run_queue() get_device() under host lock will succeed. --- drivers/scsi/scsi_lib.c | 5 +++++ drivers/scsi/scsi_sysfs.c | 7 ++++++- 2 files changed, 11 insertions(+), 1 deletions(-) diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index ffd7773..bd7daec 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -452,10 +452,15 @@ static void scsi_run_queue(struct request_queue *q) continue; } + get_device(&sdev->sdev_gendev); spin_unlock(shost->host_lock); + spin_lock(sdev->request_queue->queue_lock); __blk_run_queue(sdev->request_queue); spin_unlock(sdev->request_queue->queue_lock); + + put_device(&sdev->sdev_gendev); + spin_lock(shost->host_lock); } /* put any unprocessed entries back */ diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index 093d4f6..44f232e 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -348,7 +348,6 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work) starget->reap_ref++; list_del(&sdev->siblings); list_del(&sdev->same_target_siblings); - list_del(&sdev->starved_entry); spin_unlock_irqrestore(sdev->host->host_lock, flags); cancel_work_sync(&sdev->event_work); @@ -956,6 +955,8 @@ int scsi_sysfs_add_sdev(struct scsi_device *sdev) void __scsi_remove_device(struct scsi_device *sdev) { struct device *dev = &sdev->sdev_gendev; + struct Scsi_Host *shost = sdev->host; + unsigned long flags; if (sdev->is_visible) { if (scsi_device_set_state(sdev, SDEV_CANCEL) != 0) @@ -977,6 +978,10 @@ void __scsi_remove_device(struct scsi_device *sdev) blk_cleanup_queue(sdev->request_queue); cancel_work_sync(&sdev->requeue_work); + spin_lock_irqsave(shost->host_lock, flags); + list_del(&sdev->starved_entry); + spin_unlock_irqrestore(shost->host_lock, flags); + if (sdev->host->hostt->slave_destroy) sdev->host->hostt->slave_destroy(sdev); transport_destroy_device(dev); -- 1.7.7