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 <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>
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@ -594,10 +594,11 @@ static void transport_lun_remove_cmd(struct se_cmd *cmd)
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{
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struct se_lun *lun = cmd->se_lun;
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if (!lun || !cmd->lun_ref_active)
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if (!lun)
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return;
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percpu_ref_put(&lun->lun_ref);
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if (cmpxchg(&cmd->lun_ref_active, true, false))
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percpu_ref_put(&lun->lun_ref);
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}
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void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
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@ -552,7 +552,7 @@ struct se_cmd {
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void *priv;
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/* Used for lun->lun_ref counting */
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bool lun_ref_active;
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int lun_ref_active;
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/* DIF related members */
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enum target_prot_op prot_op;
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