Author: hselasky
Date: Wed Dec 18 09:30:32 2019
New Revision: 355879
URL: https://svnweb.freebsd.org/changeset/base/355879
Log:
Restore important comment in RCU/EPOCH support in FreeBSD after r355784.
Sponsored by: Mellanox Technologies
Modified:
head/sys/compat/linuxkpi/common/src/linux_rcu.c
head/sys/kern/subr_epoch.c
Modified: head/sys/compat/linuxkpi/common/src/linux_rcu.c
==============================================================================
--- head/sys/compat/linuxkpi/common/src/linux_rcu.c Wed Dec 18 08:39:24
2019 (r355878)
+++ head/sys/compat/linuxkpi/common/src/linux_rcu.c Wed Dec 18 09:30:32
2019 (r355879)
@@ -259,6 +259,15 @@ linux_synchronize_rcu_cb(ck_epoch_t *epoch __unused, c
sched_prio(td, prio);
/* task switch */
mi_switch(SW_VOL | SWT_RELINQUISH);
+ /*
+ * It is important the thread lock is dropped
+ * while yielding to allow other threads to
+ * acquire the lock pointed to by
+ * TDQ_LOCKPTR(td). Currently mi_switch() will
+ * unlock the thread lock before
+ * returning. Else a deadlock like situation
+ * might happen.
+ */
thread_lock(td);
}
} else {
Modified: head/sys/kern/subr_epoch.c
==============================================================================
--- head/sys/kern/subr_epoch.c Wed Dec 18 08:39:24 2019 (r355878)
+++ head/sys/kern/subr_epoch.c Wed Dec 18 09:30:32 2019 (r355879)
@@ -578,6 +578,13 @@ epoch_block_handler_preempt(struct ck_epoch *global __
*/
counter_u64_add(switch_count, 1);
mi_switch(SW_VOL | SWT_RELINQUISH);
+ /*
+ * It is important the thread lock is dropped while yielding
+ * to allow other threads to acquire the lock pointed to by
+ * TDQ_LOCKPTR(td). Currently mi_switch() will unlock the
+ * thread lock before returning. Else a deadlock like
+ * situation might happen.
+ */
thread_lock(td);
}
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