target: Fix percpu_ref_put race in transport_lun_remove_cmd

This patch fixes a percpu_ref_put race for se_lun->lun_ref in transport_lun_remove_cmd() where ->lun_ref could end up being put more than once per command via different target completion and fabric release contexts. It adds a cmpxchg() for se_cmd->lun_ref_active to ensure that percpu_ref_put() is only ever called once per se_cmd. This bug was manifesting itself as a LUN shutdown regression bug in >= v3.13 code, where percpu_ref_kill() would end up hanging indefinately due to the incorrect percpu_ref count. (Change se_cmd->lun_ref_active from bool -> int to force at least a 4-byte cmpxchg with MIPS ll/sc ins. - Fengguang) Reported-by: Tommy Apel <[email protected]> Cc: Tommy Apel <[email protected]> Cc: <[email protected]> #3.13+ Signed-off-by: Nicholas Bellinger <[email protected]>
o11s · Jan 30, 2014 · 5259a06 · 5259a06
1 parent ee291e6
commit 5259a06
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Showing 2 changed files with 4 additions and 3 deletions.
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
@@ -594,10 +594,11 @@ static void transport_lun_remove_cmd(struct se_cmd *cmd)
 {
 	struct se_lun *lun = cmd->se_lun;
 
-	if (!lun || !cmd->lun_ref_active)
+	if (!lun)
 		return;
 
-	percpu_ref_put(&lun->lun_ref);
+	if (cmpxchg(&cmd->lun_ref_active, true, false))
+		percpu_ref_put(&lun->lun_ref);
 }
 
 void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)

diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
@@ -552,7 +552,7 @@ struct se_cmd {
 	void			*priv;
 
 	/* Used for lun->lun_ref counting */
-	bool			lun_ref_active;
+	int			lun_ref_active;
 
 	/* DIF related members */
 	enum target_prot_op	prot_op;