On (01/30/15 15:52), Ganesh Mahendran wrote: > >> When I/O operation is running, that means the /dev/zram0 is > >> mounted or swaped on. Then the device could not be reset by > >> below code: > >> > >> /* Do not reset an active device! */ > >> if (bdev->bd_holders) { > >> ret = -EBUSY; > >> goto out; > >> } > >> > >> So the zram->init_lock in I/O path is to check whether the device > >> has been initialized(echo xxx > /sys/block/zram/disk_size). > >> > > Thanks for your explanation. > > > > > for mounted device (w/fs), we see initial (well, it goes up and down > > What does "w/" mean? 'with fs' > > many times while we create device, but this is not interesting here) > > ->bd_holders increment in: > > vfs_kern_mount -> mount_bdev -> blkdev_get_by_path -> blkdev_get > > > > and it goes to zero in: > > cleanup_mnt -> deactivate_super -> kill_block_super -> blkdev_put > > > > > > after umount we still have init device. so, *theoretically*, we > > can see something like > > > > CPU0 CPU1 > > umount > > reset_store > > bdev->bd_holders == 0 mount > > ... zram_make_request() > > zram_reset_device() > > In this example, the data stored in zram will be corrupted. > Since CPU0 will free meta while CPU1 is using. > right? > with out ->init_lock protection in this case we have 'free' vs. 'use' race. > > > > > w/o zram->init_lock in both zram_reset_device() and zram_make_request() > > one of CPUs will be a bit sad. > what does "w/o" mean? 'with out' -ss -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>