Suspend/resume zvol for recv and rollback

When doing recv and rollback, dsl_dataset_clone_swap_sync_impl will be
called to swap out the ds_objset and do dmu_objset_evict on the old one.
However, currently zv->zv_objset will not be swapped out accordingly, so
if anyone currently holds a fd on the zvol, we risk hitting a use-after-free.

We fix this by introducing the suspend and resume mechanism of zsb to
zv.  Before recv or rollback, we use zvol_suspend to block all access to
zv_objset and shut it down. After the recv or rollback, we use zvol_resume
to swap in zv_objset with the new ds_objset and unblock the access.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Chunwei Chen <[email protected]>
Closes #4866 
Closes #5609 

1 files changed, 5 insertions, 2 deletions

diff --git a/include/sys/zvol.h b/include/sys/zvol.h
index 2fb20fbf9..f149da977 100644
--- a/include/sys/zvol.h
+++ b/include/sys/zvol.h
@@ -35,14 +35,14 @@
 #define	SPEC_MAXOFFSET_T	((1LL << ((NBBY * sizeof (daddr32_t)) + \
 				DEV_BSHIFT - 1)) - 1)
 
-extern void *zvol_tag;
-
 extern void zvol_create_minors(spa_t *spa, const char *name, boolean_t async);
 extern void zvol_remove_minors(spa_t *spa, const char *name, boolean_t async);
 extern void zvol_rename_minors(spa_t *spa, const char *oldname,
     const char *newname, boolean_t async);
 
 #ifdef _KERNEL
+typedef struct zvol_state zvol_state_t;
+
 extern int zvol_check_volsize(uint64_t volsize, uint64_t blocksize);
 extern int zvol_check_volblocksize(const char *name, uint64_t volblocksize);
 extern int zvol_get_stats(objset_t *os, nvlist_t *nv);
@@ -51,6 +51,9 @@ extern void zvol_create_cb(objset_t *os, void *arg, cred_t *cr, dmu_tx_t *tx);
 extern int zvol_set_volsize(const char *, uint64_t);
 extern int zvol_set_volblocksize(const char *, uint64_t);
 extern int zvol_set_snapdev(const char *, zprop_source_t, uint64_t);
+extern zvol_state_t *zvol_suspend(const char *);
+extern int zvol_resume(zvol_state_t *);
+extern void *zvol_tag(zvol_state_t *);
 
 extern int zvol_init(void);
 extern void zvol_fini(void);