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SubjectRe: drivers/char/random.c line 728 BUG
On Fri, 29 Aug 2008 15:31:55 -0700
Aaron Straus <aaron@merfinllc.com> wrote:

> > - if (r == &input_pool &&
> > - r->entropy_count >= random_read_wakeup_thresh) {
> > + if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
> > wake_up_interruptible(&random_read_wait);
> > kill_fasync(&fasync, SIGIO, POLL_IN);
> > }
> > -
> > + r->entropy_count = entropy_count;
>
> Here you set the entropy_count in the pool *after* waking up the reader.
> I was a little worried the reader would find the entropy_count unchanged
> and go back to sleep.
>

Probably it doesn't matter because of the coverage of the lock but yes,
let's do the assignment first.

--- a/drivers/char/random.c~drivers-char-randomc-fix-a-race-which-can-lead-to-a-bogus-bug-fix-fix
+++ a/drivers/char/random.c
@@ -535,13 +535,13 @@ static void credit_entropy_bits(struct e
entropy_count = 0;
} else if (entropy_count > r->poolinfo->POOLBITS)
entropy_count = r->poolinfo->POOLBITS;
+ r->entropy_count = entropy_count;

/* should we wake readers? */
if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
wake_up_interruptible(&random_read_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);
}
- r->entropy_count = entropy_count;
spin_unlock_irqrestore(&r->lock, flags);
}

_


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