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Commit 5259a06e authored by Nicholas Bellinger's avatar Nicholas Bellinger
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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: default avatarTommy Apel <tommyapeldk@gmail.com>
Cc: Tommy Apel <tommyapeldk@gmail.com>
Cc: <stable@vger.kernel.org> #3.13+
Signed-off-by: default avatarNicholas Bellinger <nab@linux-iscsi.org>
parent ee291e63

drivers/target/target_core_transport.c

+3 −2
Original line number Diff line number Diff line
@@ -594,9 +594,10 @@ 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;



	if (cmpxchg(&cmd->lun_ref_active, true, false))

		percpu_ref_put(&lun->lun_ref);

}

include/target/target_core_base.h

+1 −1
Original line number Diff line number Diff line
@@ -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;