Hi Mike
Thanks very much for your analysis.
diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index 2e33100..6396581 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -684,7 +684,6 @@ static int tcmu_check_expired_cmd(int id, void *p, void *data)
set_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags);
target_complete_cmd(cmd->se_cmd, SAM_STAT_CHECK_CONDITION);
- cmd->se_cmd = NULL;
How did tcmu_handle_completion get to a point it was accessing the
se_cmd if the TCMU_CMD_BIT_EXPIRED bit was set?
Were memory accesses out
of order?
No, even using the -O3, becuase has there memory dependency ?
CPU1 set the TCMU_CMD_BIT_EXPIRED bit then cleared
cmd->se_cmd, but CPU2 copied cmd->se_cmd to se_cmd and saw it was NULL
but did not yet see the TCMU_CMD_BIT_EXPIRED bit set?
Because the debug rpms for my kernel version were lost, and the crash
tools couldn't be used to have a more accurate analysis.
It looks like, if you do the above patch, the above function will call
target_complete_cmd and tcmu_handle_completion will call it again, so we
will have a double free issue.
Maybe the best resolution is to move tcmu_handle_completion() between
spin_lock(&udev->commands_lock) and spin_unlock(&udev->commands_lock)?
Thanks.
BRs
Xiubo Li
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