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ipmi: Fix a memory ordering issue

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From a locking point of view it is safe to check waiting_msg without
a lock, but there is a memory ordering issue that causes it to
possibly not be set right when viewed from another processor.  We are
already claiming a lock right after that, move the check to inside
the lock to enforce the memory ordering.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
This commit is contained in:
Corey Minyard 2015-02-19 08:25:49 -06:00
parent d6c5dc18d8
commit 1d86e29b4a
1 changed files with 10 additions and 4 deletions
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14
drivers/char/ipmi/ipmi_si_intf.c
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@ -932,9 +932,6 @@ static void sender(void *send_info,
enum si_sm_result result; enum si_sm_result result;
unsigned long flags; unsigned long flags;
BUG_ON(smi_info->waiting_msg);
smi_info->waiting_msg = msg;
debug_timestamp("Enqueue"); debug_timestamp("Enqueue");
if (smi_info->run_to_completion) { if (smi_info->run_to_completion) {
@ -942,7 +939,7 @@ static void sender(void *send_info,
* If we are running to completion, start it and run * If we are running to completion, start it and run
* transactions until everything is clear. * transactions until everything is clear.
*/ */
smi_info->curr_msg = smi_info->waiting_msg; smi_info->curr_msg = msg;
smi_info->waiting_msg = NULL; smi_info->waiting_msg = NULL;
/* /*
@ -960,6 +957,15 @@ static void sender(void *send_info,
} }
spin_lock_irqsave(&smi_info->si_lock, flags); spin_lock_irqsave(&smi_info->si_lock, flags);
/*
* The following two lines don't need to be under the lock for
* the lock's sake, but they do need SMP memory barriers to
* avoid getting things out of order. We are already claiming
* the lock, anyway, so just do it under the lock to avoid the
* ordering problem.
*/
BUG_ON(smi_info->waiting_msg);
smi_info->waiting_msg = msg;
check_start_timer_thread(smi_info); check_start_timer_thread(smi_info);
spin_unlock_irqrestore(&smi_info->si_lock, flags); spin_unlock_irqrestore(&smi_info->si_lock, flags);
} }