| Message ID | 1a69690d615610c1dee725db7e6d81cf2db28266.1444085255.git.lduncan@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
> struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) > { > - struct device *cdev; > - struct Scsi_Host *shost = NULL; > - > - cdev = class_find_device(&shost_class, NULL, &hostnum, > - __scsi_host_match); > - if (cdev) { > - shost = scsi_host_get(class_to_shost(cdev)); > - put_device(cdev); > - } > + struct Scsi_Host *shost; > + > + spin_lock(&host_index_lock); > + shost = idr_find(&host_index_idr, hostnum); > + spin_unlock(&host_index_lock); > + > return shost; How does this actually grab a reference to the host? -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 10/06/2015 01:01 AM, Lee Duncan wrote: > Update the SCSI hosts module to use idr to manage > its host_no index instead of an ATOMIC integer. This > also allows using idr_find() to look up the SCSI > host structure given the host number. > > This means that the SCSI host number will now > be reclaimable. > > Signed-off-by: Lee Duncan <lduncan@suse.com> > --- > drivers/scsi/hosts.c | 60 +++++++++++++++++++++++++--------------------------- > 1 file changed, 29 insertions(+), 31 deletions(-) > Very nice. Reviewed-by: Hannes Reinecke <hare@suse.com> Cheers, Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 10/06/2015 02:40 AM, Christoph Hellwig wrote: >> struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) >> { >> - struct device *cdev; >> - struct Scsi_Host *shost = NULL; >> - >> - cdev = class_find_device(&shost_class, NULL, &hostnum, >> - __scsi_host_match); >> - if (cdev) { >> - shost = scsi_host_get(class_to_shost(cdev)); >> - put_device(cdev); >> - } >> + struct Scsi_Host *shost; >> + >> + spin_lock(&host_index_lock); >> + shost = idr_find(&host_index_idr, hostnum); >> + spin_unlock(&host_index_lock); >> + >> return shost; > > How does this actually grab a reference to the host? Good catch -- I should have noticed that. I will resubmit the patch.
On Tue, 2015-10-06 at 10:14 -0700, Lee Duncan wrote: > On 10/06/2015 02:40 AM, Christoph Hellwig wrote: > >> struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) > >> { > >> - struct device *cdev; > >> - struct Scsi_Host *shost = NULL; > >> - > >> - cdev = class_find_device(&shost_class, NULL, &hostnum, > >> - __scsi_host_match); > >> - if (cdev) { > >> - shost = scsi_host_get(class_to_shost(cdev)); > >> - put_device(cdev); > >> - } > >> + struct Scsi_Host *shost; > >> + > >> + spin_lock(&host_index_lock); > >> + shost = idr_find(&host_index_idr, hostnum); > >> + spin_unlock(&host_index_lock); > >> + > >> return shost; > > > > How does this actually grab a reference to the host? > > Good catch -- I should have noticed that. > > I will resubmit the patch. I'll wait to see what you produce, but I don't think, using a separate idr array, you can close the race window between lookup and get. One of the nice things about using the cdev iterator is that the get is part of the lookup process. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 10/06/2015 07:17 PM, James Bottomley wrote: > On Tue, 2015-10-06 at 10:14 -0700, Lee Duncan wrote: >> On 10/06/2015 02:40 AM, Christoph Hellwig wrote: >>>> struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) >>>> { >>>> - struct device *cdev; >>>> - struct Scsi_Host *shost = NULL; >>>> - >>>> - cdev = class_find_device(&shost_class, NULL, &hostnum, >>>> - __scsi_host_match); >>>> - if (cdev) { >>>> - shost = scsi_host_get(class_to_shost(cdev)); >>>> - put_device(cdev); >>>> - } >>>> + struct Scsi_Host *shost; >>>> + >>>> + spin_lock(&host_index_lock); >>>> + shost = idr_find(&host_index_idr, hostnum); >>>> + spin_unlock(&host_index_lock); >>>> + >>>> return shost; >>> >>> How does this actually grab a reference to the host? >> >> Good catch -- I should have noticed that. >> >> I will resubmit the patch. > > I'll wait to see what you produce, but I don't think, using a separate > idr array, you can close the race window between lookup and get. One of > the nice things about using the cdev iterator is that the get is part of > the lookup process. > Hmm. Should be possible if you free up the IDR in scsi_remove_host(), just after setting the state to SHOST_DEL. Cheers, Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, 2015-10-07 at 22:23 +0200, Hannes Reinecke wrote: > On 10/06/2015 07:17 PM, James Bottomley wrote: > > On Tue, 2015-10-06 at 10:14 -0700, Lee Duncan wrote: > >> On 10/06/2015 02:40 AM, Christoph Hellwig wrote: > >>>> struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) > >>>> { > >>>> - struct device *cdev; > >>>> - struct Scsi_Host *shost = NULL; > >>>> - > >>>> - cdev = class_find_device(&shost_class, NULL, &hostnum, > >>>> - __scsi_host_match); > >>>> - if (cdev) { > >>>> - shost = scsi_host_get(class_to_shost(cdev)); > >>>> - put_device(cdev); > >>>> - } > >>>> + struct Scsi_Host *shost; > >>>> + > >>>> + spin_lock(&host_index_lock); > >>>> + shost = idr_find(&host_index_idr, hostnum); > >>>> + spin_unlock(&host_index_lock); > >>>> + > >>>> return shost; > >>> > >>> How does this actually grab a reference to the host? > >> > >> Good catch -- I should have noticed that. > >> > >> I will resubmit the patch. > > > > I'll wait to see what you produce, but I don't think, using a separate > > idr array, you can close the race window between lookup and get. One of > > the nice things about using the cdev iterator is that the get is part of > > the lookup process. > > > Hmm. Should be possible if you free up the IDR in scsi_remove_host(), > just after setting the state to SHOST_DEL. Then all lookups fail between _del and _release which is different behaviour from current. In theory that's a very short window because we should have removed all the devices synchronously in _del, so I don't think there's any adverse consequences but it's something that would need investigating. To be honest, with the host number patch, I'm starting to come to the conclusion that if it isn't broken, don't fix it because of the risks. What are we trying to fix, anyway? The host number wrapping at 32 bits? James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c index 8bb173e01084..9dc8ff971f5a 100644 --- a/drivers/scsi/hosts.c +++ b/drivers/scsi/hosts.c @@ -33,7 +33,7 @@ #include <linux/transport_class.h> #include <linux/platform_device.h> #include <linux/pm_runtime.h> - +#include <linux/idr.h> #include <scsi/scsi_device.h> #include <scsi/scsi_host.h> #include <scsi/scsi_transport.h> @@ -41,8 +41,8 @@ #include "scsi_priv.h" #include "scsi_logging.h" - -static atomic_t scsi_host_next_hn = ATOMIC_INIT(0); /* host_no for next new host */ +static DEFINE_IDR(host_index_idr); +static DEFINE_SPINLOCK(host_index_lock); static void scsi_host_cls_release(struct device *dev) @@ -337,6 +337,10 @@ static void scsi_host_dev_release(struct device *dev) kfree(shost->shost_data); + spin_lock(&host_index_lock); + idr_remove(&host_index_idr, shost->host_no); + spin_unlock(&host_index_lock); + if (parent) put_device(parent); kfree(shost); @@ -370,6 +374,7 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize) { struct Scsi_Host *shost; gfp_t gfp_mask = GFP_KERNEL; + int index; if (sht->unchecked_isa_dma && privsize) gfp_mask |= __GFP_DMA; @@ -388,11 +393,15 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize) init_waitqueue_head(&shost->host_wait); mutex_init(&shost->scan_mutex); - /* - * subtract one because we increment first then return, but we need to - * know what the next host number was before increment - */ - shost->host_no = atomic_inc_return(&scsi_host_next_hn) - 1; + idr_preload(GFP_KERNEL); + spin_lock(&host_index_lock); + index = idr_alloc(&host_index_idr, shost, 0, 0, GFP_NOWAIT); + spin_unlock(&host_index_lock); + idr_preload_end(); + if (index < 0) + goto fail_kfree; + shost->host_no = index; + shost->dma_channel = 0xff; /* These three are default values which can be overridden */ @@ -477,7 +486,7 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize) shost_printk(KERN_WARNING, shost, "error handler thread failed to spawn, error = %ld\n", PTR_ERR(shost->ehandler)); - goto fail_kfree; + goto fail_idr_remove; } shost->tmf_work_q = alloc_workqueue("scsi_tmf_%d", @@ -493,6 +502,10 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize) fail_kthread: kthread_stop(shost->ehandler); + fail_idr_remove: + spin_lock(&host_index_lock); + idr_remove(&host_index_idr, shost->host_no); + spin_unlock(&host_index_lock); fail_kfree: kfree(shost); return NULL; @@ -522,37 +535,21 @@ void scsi_unregister(struct Scsi_Host *shost) } EXPORT_SYMBOL(scsi_unregister); -static int __scsi_host_match(struct device *dev, const void *data) -{ - struct Scsi_Host *p; - const unsigned short *hostnum = data; - - p = class_to_shost(dev); - return p->host_no == *hostnum; -} - /** * scsi_host_lookup - get a reference to a Scsi_Host by host no * @hostnum: host number to locate * * Return value: * A pointer to located Scsi_Host or NULL. - * - * The caller must do a scsi_host_put() to drop the reference - * that scsi_host_get() took. The put_device() below dropped - * the reference from class_find_device(). **/ struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) { - struct device *cdev; - struct Scsi_Host *shost = NULL; - - cdev = class_find_device(&shost_class, NULL, &hostnum, - __scsi_host_match); - if (cdev) { - shost = scsi_host_get(class_to_shost(cdev)); - put_device(cdev); - } + struct Scsi_Host *shost; + + spin_lock(&host_index_lock); + shost = idr_find(&host_index_idr, hostnum); + spin_unlock(&host_index_lock); + return shost; } EXPORT_SYMBOL(scsi_host_lookup); @@ -588,6 +585,7 @@ int scsi_init_hosts(void) void scsi_exit_hosts(void) { class_unregister(&shost_class); + idr_destroy(&host_index_idr); } int scsi_is_host_device(const struct device *dev)
Update the SCSI hosts module to use idr to manage its host_no index instead of an ATOMIC integer. This also allows using idr_find() to look up the SCSI host structure given the host number. This means that the SCSI host number will now be reclaimable. Signed-off-by: Lee Duncan <lduncan@suse.com> --- drivers/scsi/hosts.c | 60 +++++++++++++++++++++++++--------------------------- 1 file changed, 29 insertions(+), 31 deletions(-)