Messages in this thread | | | Date | Fri, 30 Jan 2015 00:12:27 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request |
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On (01/29/15 21:48), Ganesh Mahendran wrote: > > Admin could reset zram during I/O operation going on so we have > > used zram->init_lock as read-side lock in I/O path to prevent > > sudden zram meta freeing. > > 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). >
for mounted device (w/fs), we see initial (well, it goes up and down 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()
w/o zram->init_lock in both zram_reset_device() and zram_make_request() one of CPUs will be a bit sad.
-ss
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