Re: [PATCH] wait_for_completion_timeout does not return < 0

On Wed, 31 Dec 2014, Sudip Mukherjee wrote:

On Wed, Dec 31, 2014 at 04:04:03AM -0500, Nicholas Mc Guire wrote:

quoted

This is only removing the comment which is misleading as
wait_for_completion_timeout does not return < 0 thus there
never is anything to be passed on.

a small doubt - 
i am seeing that:
unsigned long wait_for_completion_timeout() is calling
long wait_for_common()  which is again calling 
long __wait_for_common which is again calling
long do_wait_for_common()

now the return value from do_wait_for_common can be -ERESTARTSYS,
so then what happens when wait_for_completion_timeout return this -ERESTARTSYS as an unsigned value ?
it becomes a positive value, and ultimately ctx.result (which is 0) is returned.
so then are we just ignoring the error value from do_wait_for_common() ?

 
ESTARTSYS only can be returned if state matches in do_wait_for_common
but wait_for_completion_timemout passes TASK_UNINTERRUPTIBLE
so signal_pending_state will return 0 and thus it will never
return -ERESTARTSYS.

my understanding of the callchain is:
wait_for_completion_timemout which is uninterruptible
  -> wait_for_common(...TASK_UNINTERRUPTIBLE)
    -> __wait_for_common(...TASK_UNINTERRUPTIBLE)
      -> do_wait_for_common(...TASK_UNINTERRUPTIBLE)
        -> signal_pending_state(TASK_UNINTERRUPTIBLE...)

static inline int signal_pending_state(long state, struct task_struct *p)
{
        if (!(state & (TASK_INTERRUPTIBLE | TASK_WAKEKILL)))
                return 0;

so wait_for_completion_timemout should return >=0 only

thx!
hofrat

quoted

patch is against linux-next 3.19.0-rc1 -next-20141226

Signed-off-by: Nicholas Mc Guire <redacted>
---
 drivers/net/wimax/i2400m/driver.c |    1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/net/wimax/i2400m/driver.c b/drivers/net/wimax/i2400m/driver.c
index 9c78090..0a6384e 100644
--- a/drivers/net/wimax/i2400m/driver.c
+++ b/drivers/net/wimax/i2400m/driver.c

@@ -197,7 +197,6 @@ int i2400m_op_reset(struct wimax_dev *wimax_dev)
 		result = -ETIMEDOUT;
 	else if (result > 0)
 		result = ctx.result;
-	/* if result < 0, pass it on */
 	mutex_lock(&i2400m->init_mutex);
 	i2400m->reset_ctx = NULL;
 	mutex_unlock(&i2400m->init_mutex);

-- 
1.7.10.4

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