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scst_user, rt: Wake command processing thread when needed

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In a fully-preemptible realtime kernel (CONFIG_PREEMPT_RT_FULL=y),
SCSI commands from an initiator time out because the userland target
application is never woken to process them.

This is because in a fully-preemptible realtime kernel, soft-IRQ
(tasklet) execution always occurs in a ksoftirqd thread and
preempt_count is not manipulated on soft-IRQ processing entry/exit.
This makes in_interrupt() useless for determining whether soft-IRQ
processing is occurring; instead, in_serving_softirq() should be
used for that purpose.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
[bvanassche: Elaborated source code comment]


git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@5272 d57e44dd-8a1f-0410-8b47-8ef2f437770f
This commit is contained in:
Bart Van Assche
2014-02-07 12:43:25 +00:00
parent ad681d7c5a
commit 91d9391194
1 changed files with 6 additions and 1 deletions
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7
scst/src/dev_handlers/scst_user.c
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@@ -1129,7 +1129,12 @@ static void dev_user_add_to_ready(struct scst_user_cmd *ucmd)
{
struct scst_user_dev *dev = ucmd->dev;
unsigned long flags;
int do_wake = in_interrupt();
/*
* Note, a separate softIRQ check is required for real-time kernels
* (CONFIG_PREEMPT_RT_FULL=y) since on such kernels softIRQ's are
* served in thread context. See also http://lwn.net/Articles/302043/.
*/
int do_wake = in_interrupt() || in_serving_softirq();
TRACE_ENTRY();