On 8/10/21 3:41 PM, Scott Long wrote:
The branch main has been updated by scottl:
URL:
https://cgit.FreeBSD.org/src/commit/?id=35547df5c78653b2da030f920323c0357056099f
commit 35547df5c78653b2da030f920323c0357056099f
Author: Scott Long <sco...@freebsd.org>
AuthorDate: 2021-08-10 22:36:38 +0000
Commit: Scott Long <sco...@freebsd.org>
CommitDate: 2021-08-10 22:36:38 +0000
Call wakeup() with the lock held to avoid missed wakeup races.
Submitted by: luiz
Sponsored by: Rubicon Communications, LLC ("Netgate")
---
sys/dev/sdhci/sdhci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/sys/dev/sdhci/sdhci.c b/sys/dev/sdhci/sdhci.c
index d075c2e05000..573e6949b57e 100644
--- a/sys/dev/sdhci/sdhci.c
+++ b/sys/dev/sdhci/sdhci.c
@@ -2078,8 +2078,8 @@ sdhci_generic_release_host(device_t brdev __unused,
device_t reqdev)
/* Deactivate led. */
WR1(slot, SDHCI_HOST_CONTROL, slot->hostctrl &= ~SDHCI_CTRL_LED);
slot->bus_busy--;
- SDHCI_UNLOCK(slot);
wakeup(slot);
+ SDHCI_UNLOCK(slot);
return (0);
}
Hmm, how does this avoid a race? The sleep is checking bus_busy under
the lock and should never see a stale value and go back to sleep after
the wakeup has occurred:
SDHCI_LOCK(slot);
while (slot->bus_busy)
msleep(slot, &slot->mtx, 0, "sdhciah", 0);
slot->bus_busy++;
/* Activate led. */
WR1(slot, SDHCI_HOST_CONTROL, slot->hostctrl |= SDHCI_CTRL_LED);
SDHCI_UNLOCK(slot);
Dropping the lock before wakeup() is a tiny optimization that avoids
having the second thread wakeup and immediately block on the lock before
it has been released by the first thread.
--
John Baldwin
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