Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 3.13 087/120] target: Fix percpu_ref_put race in transport_lun_remove_cmd | Date | Tue, 11 Feb 2014 11:05:28 -0800 |
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3.13-stable review patch. If anyone has any objections, please let me know.
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From: Nicholas Bellinger <nab@linux-iscsi.org>
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 <tommyapeldk@gmail.com> Cc: Tommy Apel <tommyapeldk@gmail.com> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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 {
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