diff options
| author | Tim Chase <[email protected]> | 2014-05-08 09:51:01 -0500 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2014-05-19 11:45:11 -0700 |
| commit | 3937ab20f32fc7b79cacfd91c0891f4e1b4ab2de (patch) | |
| tree | 485d588f306837e2d2d271d1b3cc01cd1d67d2e8 /include/sys/zfs_ioctl.h | |
| parent | 1cbae971c5ef215d1036b65511a839879e446c4c (diff) | |
Allow for lock-free reading zfsdev_state_list.
Restructure the zfsdev_state_list to allow for lock-free reading by
converting to a simple singly-linked list from which items are never
deleted and over which only forward iterations are performed. It depends
on, among other things, the atomicity of accessing the zs_minor integer
and zs_next pointer.
This fixes a lock inversion in which the zfsdev_state_lock is used by
both the sync task (txg_sync) and indirectly by any user program which
uses /dev/zfs; the zfsdev_release method uses the same lock and then
blocks on the sync task.
The most typical failure scenerio occurs when the sync task is cleaning
up a user hold while various concurrent "zfs" commands are in progress.
Neither Illumos nor Solaris are affected by this issue because they use
DDI interface which provides lock-free reading of device state via the
ddi_get_soft_state() function.
Signed-off-by: Tim Chase <[email protected]>
Signed-off-by: Chunwei Chen <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2301
Diffstat (limited to 'include/sys/zfs_ioctl.h')
| -rw-r--r-- | include/sys/zfs_ioctl.h | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/include/sys/zfs_ioctl.h b/include/sys/zfs_ioctl.h index 0ab095c1a..c7bd789e8 100644 --- a/include/sys/zfs_ioctl.h +++ b/include/sys/zfs_ioctl.h @@ -371,8 +371,15 @@ enum zfsdev_state_type { ZST_ALL, }; +/* + * The zfsdev_state_t structure is managed as a singly-linked list + * from which items are never deleted. This allows for lock-free + * reading of the list so long as assignments to the zs_next and + * reads from zs_minor are performed atomically. Empty items are + * indicated by storing -1 into zs_minor. + */ typedef struct zfsdev_state { - list_node_t zs_next; /* next zfsdev_state_t link */ + struct zfsdev_state *zs_next; /* next zfsdev_state_t link */ struct file *zs_file; /* associated file struct */ minor_t zs_minor; /* made up minor number */ void *zs_onexit; /* onexit data */ |