svn commit: r349476 - in head/sys: kern sys
Rick Macklem
rmacklem at FreeBSD.org
Thu Jun 27 23:10:42 UTC 2019
Author: rmacklem
Date: Thu Jun 27 23:10:40 2019
New Revision: 349476
URL: https://svnweb.freebsd.org/changeset/base/349476
Log:
Add non-blocking trylock variants for the rangelock functions.
A future patch that will add a Linux compatible copy_file_range(2) syscall
needs to be able to lock the byte ranges of two files concurrently.
To do this without a risk of deadlock, a non-blocking variant of
vn_rangelock_rlock() called vn_rangelock_tryrlock() was needed.
This patch adds this, along with vn_rangelock_trywlock(), in order to
do this.
The patch also adds a couple of comments, that I hope clarify how the
algorithm used in kern_rangelock.c works.
Reviewed by: kib, asomers (previous version)
Differential Revision: https://reviews.freebsd.org/D20645
Modified:
head/sys/kern/kern_rangelock.c
head/sys/sys/rangelock.h
head/sys/sys/vnode.h
Modified: head/sys/kern/kern_rangelock.c
==============================================================================
--- head/sys/kern/kern_rangelock.c Thu Jun 27 22:50:11 2019 (r349475)
+++ head/sys/kern/kern_rangelock.c Thu Jun 27 23:10:40 2019 (r349476)
@@ -141,15 +141,33 @@ out:
static void
rangelock_unlock_locked(struct rangelock *lock, struct rl_q_entry *entry,
- struct mtx *ilk)
+ struct mtx *ilk, bool do_calc_block)
{
MPASS(lock != NULL && entry != NULL && ilk != NULL);
mtx_assert(ilk, MA_OWNED);
- KASSERT(entry != lock->rl_currdep, ("stuck currdep"));
+ if (!do_calc_block) {
+ /*
+ * This is the case where rangelock_enqueue() has been called
+ * with trylock == true and just inserted this entry in the
+ * queue.
+ * If rl_currdep is this entry, rl_currdep needs to
+ * be set to the next entry in the rl_waiters list.
+ * However, since this entry is the last entry in the
+ * list, the next entry is NULL.
+ */
+ if (lock->rl_currdep == entry) {
+ KASSERT(TAILQ_NEXT(lock->rl_currdep, rl_q_link) == NULL,
+ ("rangelock_enqueue: next entry not NULL"));
+ lock->rl_currdep = NULL;
+ }
+ } else
+ KASSERT(entry != lock->rl_currdep, ("stuck currdep"));
+
TAILQ_REMOVE(&lock->rl_waiters, entry, rl_q_link);
- rangelock_calc_block(lock);
+ if (do_calc_block)
+ rangelock_calc_block(lock);
mtx_unlock(ilk);
if (curthread->td_rlqe == NULL)
curthread->td_rlqe = entry;
@@ -164,7 +182,7 @@ rangelock_unlock(struct rangelock *lock, void *cookie,
MPASS(lock != NULL && cookie != NULL && ilk != NULL);
mtx_lock(ilk);
- rangelock_unlock_locked(lock, cookie, ilk);
+ rangelock_unlock_locked(lock, cookie, ilk, true);
}
/*
@@ -185,7 +203,7 @@ rangelock_unlock_range(struct rangelock *lock, void *c
mtx_lock(ilk);
if (entry->rl_q_end == end) {
- rangelock_unlock_locked(lock, cookie, ilk);
+ rangelock_unlock_locked(lock, cookie, ilk, true);
return (NULL);
}
entry->rl_q_end = end;
@@ -196,11 +214,11 @@ rangelock_unlock_range(struct rangelock *lock, void *c
/*
* Add the lock request to the queue of the pending requests for
- * rangelock. Sleep until the request can be granted.
+ * rangelock. Sleep until the request can be granted unless trylock == true.
*/
static void *
rangelock_enqueue(struct rangelock *lock, off_t start, off_t end, int mode,
- struct mtx *ilk)
+ struct mtx *ilk, bool trylock)
{
struct rl_q_entry *entry;
struct thread *td;
@@ -226,11 +244,28 @@ rangelock_enqueue(struct rangelock *lock, off_t start,
*/
TAILQ_INSERT_TAIL(&lock->rl_waiters, entry, rl_q_link);
+ /*
+ * If rl_currdep == NULL, there is no entry waiting for a conflicting
+ * range to be resolved, so set rl_currdep to this entry. If there is
+ * no conflicting entry for this entry, rl_currdep will be set back to
+ * NULL by rangelock_calc_block().
+ */
if (lock->rl_currdep == NULL)
lock->rl_currdep = entry;
rangelock_calc_block(lock);
- while (!(entry->rl_q_flags & RL_LOCK_GRANTED))
+ while (!(entry->rl_q_flags & RL_LOCK_GRANTED)) {
+ if (trylock) {
+ /*
+ * For this case, the range is not actually locked
+ * yet, but removal from the list requires the same
+ * steps, except for not doing a rangelock_calc_block()
+ * call, since rangelock_calc_block() was called above.
+ */
+ rangelock_unlock_locked(lock, entry, ilk, false);
+ return (NULL);
+ }
msleep(entry, ilk, 0, "range", 0);
+ }
mtx_unlock(ilk);
return (entry);
}
@@ -239,12 +274,28 @@ void *
rangelock_rlock(struct rangelock *lock, off_t start, off_t end, struct mtx *ilk)
{
- return (rangelock_enqueue(lock, start, end, RL_LOCK_READ, ilk));
+ return (rangelock_enqueue(lock, start, end, RL_LOCK_READ, ilk, false));
}
void *
+rangelock_tryrlock(struct rangelock *lock, off_t start, off_t end,
+ struct mtx *ilk)
+{
+
+ return (rangelock_enqueue(lock, start, end, RL_LOCK_READ, ilk, true));
+}
+
+void *
rangelock_wlock(struct rangelock *lock, off_t start, off_t end, struct mtx *ilk)
{
- return (rangelock_enqueue(lock, start, end, RL_LOCK_WRITE, ilk));
+ return (rangelock_enqueue(lock, start, end, RL_LOCK_WRITE, ilk, false));
+}
+
+void *
+rangelock_trywlock(struct rangelock *lock, off_t start, off_t end,
+ struct mtx *ilk)
+{
+
+ return (rangelock_enqueue(lock, start, end, RL_LOCK_WRITE, ilk, true));
}
Modified: head/sys/sys/rangelock.h
==============================================================================
--- head/sys/sys/rangelock.h Thu Jun 27 22:50:11 2019 (r349475)
+++ head/sys/sys/rangelock.h Thu Jun 27 23:10:40 2019 (r349476)
@@ -75,7 +75,11 @@ void *rangelock_unlock_range(struct rangelock *lock, v
off_t start, off_t end, struct mtx *ilk);
void *rangelock_rlock(struct rangelock *lock, off_t start, off_t end,
struct mtx *ilk);
+void *rangelock_tryrlock(struct rangelock *lock, off_t start, off_t end,
+ struct mtx *ilk);
void *rangelock_wlock(struct rangelock *lock, off_t start, off_t end,
+ struct mtx *ilk);
+void *rangelock_trywlock(struct rangelock *lock, off_t start, off_t end,
struct mtx *ilk);
void rlqentry_free(struct rl_q_entry *rlqe);
Modified: head/sys/sys/vnode.h
==============================================================================
--- head/sys/sys/vnode.h Thu Jun 27 22:50:11 2019 (r349475)
+++ head/sys/sys/vnode.h Thu Jun 27 23:10:40 2019 (r349476)
@@ -720,8 +720,12 @@ int vn_io_fault_pgmove(vm_page_t ma[], vm_offset_t off
VI_MTX(vp))
#define vn_rangelock_rlock(vp, start, end) \
rangelock_rlock(&(vp)->v_rl, (start), (end), VI_MTX(vp))
+#define vn_rangelock_tryrlock(vp, start, end) \
+ rangelock_tryrlock(&(vp)->v_rl, (start), (end), VI_MTX(vp))
#define vn_rangelock_wlock(vp, start, end) \
rangelock_wlock(&(vp)->v_rl, (start), (end), VI_MTX(vp))
+#define vn_rangelock_trywlock(vp, start, end) \
+ rangelock_trywlock(&(vp)->v_rl, (start), (end), VI_MTX(vp))
int vfs_cache_lookup(struct vop_lookup_args *ap);
void vfs_timestamp(struct timespec *);
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