From 51a858817dcdbbdee22cb54b0b2b26eb145ca5b6 Mon Sep 17 00:00:00 2001 From: Merlijn Wajer Date: Tue, 18 Feb 2020 15:39:17 +0100 Subject: [PATCH] scsi: sr: get rid of sr global mutex 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 Signed-off-by: Merlijn Wajer Signed-off-by: Martin K. Petersen --- drivers/scsi/sr.c | 20 +++++++++++--------- drivers/scsi/sr.h | 2 ++ 2 files changed, 13 insertions(+), 9 deletions(-) diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c index 0fbb8fe..fe0e1c7 100644 --- 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_device *bdev, fmode_t mode) 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_device *bdev, fmode_t mode, unsigned cmd, 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 block_device *bdev, fmode_t mode, unsign 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 *kref) put_disk(disk); + mutex_destroy(&cd->lock); + kfree(cd); } diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h index a2bb7b8..339c624 100644 --- a/drivers/scsi/sr.h +++ b/drivers/scsi/sr.h @@ -20,6 +20,7 @@ #include #include +#include #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; -- 2.7.4