From: Merlijn Wajer merlijn@archive.org
commit 51a858817dcdbbdee22cb54b0b2b26eb145ca5b6 upstream.
When replacing the Big Kernel Lock in commit 2a48fc0ab242 ("block: autoconvert trivial BKL users to private mutex"), the lock was replaced with a sr-wide lock.
This causes very poor performance when using multiple sr devices, as the sr driver was not able to execute more than one command to one drive at any given time, even when there were many CD drives available.
Replace the global mutex with per-sr-device mutex.
Someone tried this patch at the time, but it never made it upstream, due to possible concerns with race conditions, but it's not clear the patch actually caused those:
https://www.spinics.net/lists/linux-scsi/msg63706.html https://www.spinics.net/lists/linux-scsi/msg63750.html
Also see
http://lists.xiph.org/pipermail/paranoia/2019-December/001647.html
Link: https://lore.kernel.org/r/20200218143918.30267-1-merlijn@archive.org Acked-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Merlijn Wajer merlijn@archive.org Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/scsi/sr.c | 20 +++++++++++--------- drivers/scsi/sr.h | 2 ++ 2 files changed, 13 insertions(+), 9 deletions(-)
--- a/drivers/scsi/sr.c +++ b/drivers/scsi/sr.c @@ -79,7 +79,6 @@ MODULE_ALIAS_SCSI_DEVICE(TYPE_WORM); CDC_CD_R|CDC_CD_RW|CDC_DVD|CDC_DVD_R|CDC_DVD_RAM|CDC_GENERIC_PACKET| \ CDC_MRW|CDC_MRW_W|CDC_RAM)
-static DEFINE_MUTEX(sr_mutex); static int sr_probe(struct device *); static int sr_remove(struct device *); static blk_status_t sr_init_command(struct scsi_cmnd *SCpnt); @@ -536,9 +535,9 @@ static int sr_block_open(struct block_de scsi_autopm_get_device(sdev); check_disk_change(bdev);
- mutex_lock(&sr_mutex); + mutex_lock(&cd->lock); ret = cdrom_open(&cd->cdi, bdev, mode); - mutex_unlock(&sr_mutex); + mutex_unlock(&cd->lock);
scsi_autopm_put_device(sdev); if (ret) @@ -551,10 +550,10 @@ out: static void sr_block_release(struct gendisk *disk, fmode_t mode) { struct scsi_cd *cd = scsi_cd(disk); - mutex_lock(&sr_mutex); + mutex_lock(&cd->lock); cdrom_release(&cd->cdi, mode); scsi_cd_put(cd); - mutex_unlock(&sr_mutex); + mutex_unlock(&cd->lock); }
static int sr_block_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd, @@ -565,7 +564,7 @@ static int sr_block_ioctl(struct block_d void __user *argp = (void __user *)arg; int ret;
- mutex_lock(&sr_mutex); + mutex_lock(&cd->lock);
ret = scsi_ioctl_block_when_processing_errors(sdev, cmd, (mode & FMODE_NDELAY) != 0); @@ -595,7 +594,7 @@ put: scsi_autopm_put_device(sdev);
out: - mutex_unlock(&sr_mutex); + mutex_unlock(&cd->lock); return ret; }
@@ -608,7 +607,7 @@ static int sr_block_compat_ioctl(struct void __user *argp = compat_ptr(arg); int ret;
- mutex_lock(&sr_mutex); + mutex_lock(&cd->lock);
ret = scsi_ioctl_block_when_processing_errors(sdev, cmd, (mode & FMODE_NDELAY) != 0); @@ -638,7 +637,7 @@ put: scsi_autopm_put_device(sdev);
out: - mutex_unlock(&sr_mutex); + mutex_unlock(&cd->lock); return ret;
} @@ -745,6 +744,7 @@ static int sr_probe(struct device *dev) disk = alloc_disk(1); if (!disk) goto fail_free; + mutex_init(&cd->lock);
spin_lock(&sr_index_lock); minor = find_first_zero_bit(sr_index_bits, SR_DISKS); @@ -1055,6 +1055,8 @@ static void sr_kref_release(struct kref
put_disk(disk);
+ mutex_destroy(&cd->lock); + kfree(cd); }
--- a/drivers/scsi/sr.h +++ b/drivers/scsi/sr.h @@ -20,6 +20,7 @@
#include <linux/genhd.h> #include <linux/kref.h> +#include <linux/mutex.h>
#define MAX_RETRIES 3 #define SR_TIMEOUT (30 * HZ) @@ -51,6 +52,7 @@ typedef struct scsi_cd { bool ignore_get_event:1; /* GET_EVENT is unreliable, use TUR */
struct cdrom_device_info cdi; + struct mutex lock; /* We hold gendisk and scsi_device references on probe and use * the refs on this kref to decide when to release them */ struct kref kref;