Update SCSI hosts to use idr for host number mgmt
v2 cover Update SCSI hosts to use idr for host number mgmt
This patch updates the SCSI hosts module to use the idr index-management routines to manage its host_no index instead of using an ATOMIC integer. This means that host numbers can now be reclaimed and re-used.
It also updates the hosts module to use the idr routine idr_find() to lookup hosts based on the host number, hopefully speeding up said lookup.
After noticing that my idr calling sequences where very close to those in other modules, I considered creating some idr helper functions (and using them), but because idr usage almost always requires the caller to manage their own locks, I gave up on this approach (as suggested by Tejon -- thank you).
Lee Duncan (1):
SCSI: update hosts module to use idr index management
drivers/scsi/hosts.c | 60 +++++++++++++++++++++++++--------------------------- 1 file changed, 29 insertions(+), 31 deletions(-)
Signature · 1 line
2.1.4
PATCH v2 1/1 SCSI: update hosts module to use idr index management
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.
--- drivers/scsi/hosts.c | 60 +++++++++++++++++++++++++--------------------------- 1 file changed, 29 insertions(+), 31 deletions(-)
drivers/scsi/hosts.c +29 -31
@@ -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)
Signature · 1 line
2.1.4
Re: [PATCHv2 1/1] SCSI: update hosts module to use idr index management
Quoted 8 lines
struct
Scsi_Host*scsi_host_lookup(unsigned short hostnum) {drivers/scsi/hosts.c +0
-6-struct device *cdev; -struct Scsi_Host *shost =NULL ; - - cdev =class_find_device (&shost_class,NULL , &hostnum, - __scsi_host_match); -if (cdev) {
drivers/scsi/hosts.c void scsi_unregister(struct Scsi_Host *shost) · line 553
Quoted 10 lines
drivers/scsi/hosts.c +6
-3- 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?
Re: [PATCHv2 1/1] SCSI: update hosts module to use idr index management
Quoted 12 lines · Christoph Hellwig
Quoted 12 lines
struct
Scsi_Host*scsi_host_lookup(unsigned short hostnum) {drivers/scsi/hosts.c +1
-9-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;
Quoted 8 lines
drivers/scsi/hosts.c void scsi_unregister(struct Scsi_Host *shost) · line 553
Quoted 6 lines
drivers/scsi/hosts.c +5
-0+ +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.
Signature · 1 line
Lee Duncan
James Bottomley
maintainerRe: [PATCHv2 1/1] SCSI: update hosts module to use idr index management
Quoted 22 lines · Lee Duncan
Quoted 12 lines · Christoph Hellwig
Quoted 12 lines
struct
Scsi_Host*scsi_host_lookup(unsigned short hostnum) {drivers/scsi/hosts.c +1
-9-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;Quoted 8 lines
drivers/scsi/hosts.c void scsi_unregister(struct Scsi_Host *shost) · line 553
Quoted 6 lines
drivers/scsi/hosts.c +5
-0+ +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?
Quoted 3 lines
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
Re: [PATCHv2 1/1] SCSI: update hosts module to use idr index management
Quoted 23 lines · James Bottomley
Quoted 22 lines · Lee Duncan
Quoted 20 lines · Christoph Hellwig
Quoted 8 lines
struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) {drivers/scsi/hosts.c +0
-6-struct device *cdev; -struct Scsi_Host *shost =NULL ; - - cdev =class_find_device (&shost_class,NULL , &hostnum, - __scsi_host_match); -if (cdev) {drivers/scsi/hosts.c void scsi_unregister(struct Scsi_Host *shost) · line 553
Quoted 10 lines
drivers/scsi/hosts.c +6
-3- 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?
Quoted 9 lines
Quoted 3 lines
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
James Bottomley
maintainerRe: [PATCHv2 1/1] SCSI: update hosts module to use idr index management
Quoted 28 lines · Hannes Reinecke
Quoted 27 lines · James Bottomley
Quoted 25 lines · Lee Duncan
Quoted 12 lines · Christoph Hellwig
Quoted 12 lines
struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) {drivers/scsi/hosts.c +1
-9-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;Quoted 8 lines
drivers/scsi/hosts.c void scsi_unregister(struct Scsi_Host *shost) · line 553
Quoted 6 lines
drivers/scsi/hosts.c +5
-0+ +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.
Quoted 7 lines
Quoted 5 lines
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 toSHOST_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
Re: [PATCHv2 1/1] SCSI: update hosts module to use idr index management
In reply to Lee DuncanQuoted 5 lines · Lee Duncan
Update the SCSI hosts module to use idr to manage its
host_noindex instead of an ATOMIC integer. This also allows usingidr_find()to look up the SCSI host structure given the host number.
Quoted 8 lines
This means that the SCSI host number will now be reclaimable.
Signed-off-by Lee Duncan <[email protected]>--- drivers/scsi/hosts.c | 60 +++++++++++++++++++++++++--------------------------- 1 file changed, 29 insertions(+), 31 deletions(-)
Very nice.
Cheers,
Hannes