| Message ID | 20201116145809.410558-61-hch@lst.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/78] block: remove the call to __invalidate_device in check_disk_size_change | expand |
On 11/16/20 3:57 PM, Christoph Hellwig wrote: > The zram claim mechanism was added to ensure no new opens come in > during teardown. But the proper way to archive that is to call > del_gendisk first, which takes care of all that. Once del_gendisk > is called in the right place, the reset side can also be simplified > as no I/O can be outstanding on a block device that is not open. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > drivers/block/zram/zram_drv.c | 76 ++++++++++------------------------- > 1 file changed, 21 insertions(+), 55 deletions(-) > Reviewed-by: Hannes Reinecke <hare@suse.de> Cheers, Hannes
On Mon, Nov 16, 2020 at 03:57:51PM +0100, Christoph Hellwig wrote: > The zram claim mechanism was added to ensure no new opens come in > during teardown. But the proper way to archive that is to call > del_gendisk first, which takes care of all that. Once del_gendisk > is called in the right place, the reset side can also be simplified > as no I/O can be outstanding on a block device that is not open. It would be great if it makes the mess simple. Let me have a question Please see below. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > drivers/block/zram/zram_drv.c | 76 ++++++++++------------------------- > 1 file changed, 21 insertions(+), 55 deletions(-) > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 6d15d51cee2b7e..3641434a9b154d 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -1756,64 +1756,33 @@ static ssize_t disksize_store(struct device *dev, > static ssize_t reset_store(struct device *dev, > struct device_attribute *attr, const char *buf, size_t len) > { > - int ret; > - unsigned short do_reset; > - struct zram *zram; > + struct zram *zram = dev_to_zram(dev); > struct block_device *bdev; > + unsigned short do_reset; > + int ret = 0; > > ret = kstrtou16(buf, 10, &do_reset); > if (ret) > return ret; > - > if (!do_reset) > return -EINVAL; > > - zram = dev_to_zram(dev); > bdev = bdget_disk(zram->disk, 0); > if (!bdev) > return -ENOMEM; > > mutex_lock(&bdev->bd_mutex); > - /* Do not reset an active device or claimed device */ > - if (bdev->bd_openers || zram->claim) { > - mutex_unlock(&bdev->bd_mutex); > - bdput(bdev); > - return -EBUSY; > - } > - > - /* From now on, anyone can't open /dev/zram[0-9] */ > - zram->claim = true; > + if (bdev->bd_openers) > + ret = -EBUSY; > + else > + zram_reset_device(zram); > mutex_unlock(&bdev->bd_mutex); > - > - /* Make sure all the pending I/O are finished */ > - fsync_bdev(bdev); > - zram_reset_device(zram); > bdput(bdev); > > - mutex_lock(&bdev->bd_mutex); > - zram->claim = false; > - mutex_unlock(&bdev->bd_mutex); > - > - return len; > -} > - > -static int zram_open(struct block_device *bdev, fmode_t mode) > -{ > - int ret = 0; > - struct zram *zram; > - > - WARN_ON(!mutex_is_locked(&bdev->bd_mutex)); > - > - zram = bdev->bd_disk->private_data; > - /* zram was claimed to reset so open request fails */ > - if (zram->claim) > - ret = -EBUSY; > - > - return ret; > + return ret ? ret : len; > } > > static const struct block_device_operations zram_devops = { > - .open = zram_open, > .submit_bio = zram_submit_bio, > .swap_slot_free_notify = zram_slot_free_notify, > .rw_page = zram_rw_page, > @@ -1821,7 +1790,6 @@ static const struct block_device_operations zram_devops = { > }; > > static const struct block_device_operations zram_wb_devops = { > - .open = zram_open, > .submit_bio = zram_submit_bio, > .swap_slot_free_notify = zram_slot_free_notify, > .owner = THIS_MODULE > @@ -1972,34 +1940,32 @@ static int zram_add(void) > return ret; > } > > -static int zram_remove(struct zram *zram) > +static bool zram_busy(struct zram *zram) > { > struct block_device *bdev; > + bool busy = false; > > bdev = bdget_disk(zram->disk, 0); > - if (!bdev) > - return -ENOMEM; > - > - mutex_lock(&bdev->bd_mutex); > - if (bdev->bd_openers || zram->claim) { > - mutex_unlock(&bdev->bd_mutex); > + if (bdev) { > + if (bdev->bd_openers) > + busy = true; > bdput(bdev); > - return -EBUSY; > } > > - zram->claim = true; > - mutex_unlock(&bdev->bd_mutex); > + return busy; > +} > > - zram_debugfs_unregister(zram); > +static int zram_remove(struct zram *zram) > +{ > + if (zram_busy(zram)) > + return -EBUSY; > > - /* Make sure all the pending I/O are finished */ > - fsync_bdev(bdev); > + del_gendisk(zram->disk); > + zram_debugfs_unregister(zram); > zram_reset_device(zram); > - bdput(bdev); > > pr_info("Removed device: %s\n", zram->disk->disk_name); > > - del_gendisk(zram->disk); > blk_cleanup_queue(zram->disk->queue); > put_disk(zram->disk); > kfree(zram); > -- > 2.29.2 > With this patch, how deal with the race? CPU 1 CPU 2 hot_remove_store zram_remove zram_busy return -EBUSY open /dev/zram0 del_gendisk zram_reset and destroy
On Wed, Nov 25, 2020 at 05:11:07PM -0800, Minchan Kim wrote: > With this patch, how deal with the race? > > CPU 1 CPU 2 > > hot_remove_store > zram_remove > zram_busy > return -EBUSY > open /dev/zram0 > del_gendisk > zram_reset and destroy Yeah, it looks like zram does not really handle hot unplugging unlike other drivers. So I've dropped this one for now.
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 6d15d51cee2b7e..3641434a9b154d 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1756,64 +1756,33 @@ static ssize_t disksize_store(struct device *dev, static ssize_t reset_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t len) { - int ret; - unsigned short do_reset; - struct zram *zram; + struct zram *zram = dev_to_zram(dev); struct block_device *bdev; + unsigned short do_reset; + int ret = 0; ret = kstrtou16(buf, 10, &do_reset); if (ret) return ret; - if (!do_reset) return -EINVAL; - zram = dev_to_zram(dev); bdev = bdget_disk(zram->disk, 0); if (!bdev) return -ENOMEM; mutex_lock(&bdev->bd_mutex); - /* Do not reset an active device or claimed device */ - if (bdev->bd_openers || zram->claim) { - mutex_unlock(&bdev->bd_mutex); - bdput(bdev); - return -EBUSY; - } - - /* From now on, anyone can't open /dev/zram[0-9] */ - zram->claim = true; + if (bdev->bd_openers) + ret = -EBUSY; + else + zram_reset_device(zram); mutex_unlock(&bdev->bd_mutex); - - /* Make sure all the pending I/O are finished */ - fsync_bdev(bdev); - zram_reset_device(zram); bdput(bdev); - mutex_lock(&bdev->bd_mutex); - zram->claim = false; - mutex_unlock(&bdev->bd_mutex); - - return len; -} - -static int zram_open(struct block_device *bdev, fmode_t mode) -{ - int ret = 0; - struct zram *zram; - - WARN_ON(!mutex_is_locked(&bdev->bd_mutex)); - - zram = bdev->bd_disk->private_data; - /* zram was claimed to reset so open request fails */ - if (zram->claim) - ret = -EBUSY; - - return ret; + return ret ? ret : len; } static const struct block_device_operations zram_devops = { - .open = zram_open, .submit_bio = zram_submit_bio, .swap_slot_free_notify = zram_slot_free_notify, .rw_page = zram_rw_page, @@ -1821,7 +1790,6 @@ static const struct block_device_operations zram_devops = { }; static const struct block_device_operations zram_wb_devops = { - .open = zram_open, .submit_bio = zram_submit_bio, .swap_slot_free_notify = zram_slot_free_notify, .owner = THIS_MODULE @@ -1972,34 +1940,32 @@ static int zram_add(void) return ret; } -static int zram_remove(struct zram *zram) +static bool zram_busy(struct zram *zram) { struct block_device *bdev; + bool busy = false; bdev = bdget_disk(zram->disk, 0); - if (!bdev) - return -ENOMEM; - - mutex_lock(&bdev->bd_mutex); - if (bdev->bd_openers || zram->claim) { - mutex_unlock(&bdev->bd_mutex); + if (bdev) { + if (bdev->bd_openers) + busy = true; bdput(bdev); - return -EBUSY; } - zram->claim = true; - mutex_unlock(&bdev->bd_mutex); + return busy; +} - zram_debugfs_unregister(zram); +static int zram_remove(struct zram *zram) +{ + if (zram_busy(zram)) + return -EBUSY; - /* Make sure all the pending I/O are finished */ - fsync_bdev(bdev); + del_gendisk(zram->disk); + zram_debugfs_unregister(zram); zram_reset_device(zram); - bdput(bdev); pr_info("Removed device: %s\n", zram->disk->disk_name); - del_gendisk(zram->disk); blk_cleanup_queue(zram->disk->queue); put_disk(zram->disk); kfree(zram);
The zram claim mechanism was added to ensure no new opens come in during teardown. But the proper way to archive that is to call del_gendisk first, which takes care of all that. Once del_gendisk is called in the right place, the reset side can also be simplified as no I/O can be outstanding on a block device that is not open. Signed-off-by: Christoph Hellwig <hch@lst.de> --- drivers/block/zram/zram_drv.c | 76 ++++++++++------------------------- 1 file changed, 21 insertions(+), 55 deletions(-)