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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