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target: Fix percpu_ref_put race in transport_lun_remove_cmd

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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 <tommyapeldk@gmail.com>
Cc: Tommy Apel <tommyapeldk@gmail.com>
Cc: <stable@vger.kernel.org> #3.13+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
This commit is contained in:
Nicholas Bellinger 2014-01-28 17:56:30 -08:00
parent ee291e6329
commit 5259a06ef9
2 changed files with 4 additions and 3 deletions
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5
drivers/target/target_core_transport.c
View file

@ -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)

2
include/target/target_core_base.h
View file

@ -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;