3.13-stable review patch. If anyone has any objections, please let me know.
------------------ From: Nicholas Bellinger <[email protected]> commit 5259a06ef97068b710f45d092a587e8d740f750f upstream. 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]> Signed-off-by: Nicholas Bellinger <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- drivers/target/target_core_transport.c | 5 +++-- include/target/target_core_base.h | 2 +- 2 files changed, 4 insertions(+), 3 deletions(-) --- a/drivers/target/target_core_transport.c +++ b/drivers/target/target_core_transport.c @@ -568,10 +568,11 @@ static void transport_lun_remove_cmd(str { 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) --- a/include/target/target_core_base.h +++ b/include/target/target_core_base.h @@ -497,7 +497,7 @@ struct se_cmd { void *priv; /* Used for lun->lun_ref counting */ - bool lun_ref_active; + int lun_ref_active; }; struct se_ua { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
