svn commit: r361287 - in head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs: . sys
Mark Johnston
markj at FreeBSD.org
Wed May 20 18:29:24 UTC 2020
Author: markj
Date: Wed May 20 18:29:23 2020
New Revision: 361287
URL: https://svnweb.freebsd.org/changeset/base/361287
Log:
Don't block on the range lock in zfs_getpages().
After r358443 the vnode object lock no longer synchronizes concurrent
zfs_getpages() and zfs_write() (which must update vnode pages to
maintain coherence). This created a potential deadlock between ZFS
range locks and VM page busy locks: a fault on a mapped file will cause
the fault page to be busied, after which zfs_getpages() locks a range
around the file offset in order to map adjacent, resident pages;
zfs_write() locks the range first, and then must busy vnode pages when
synchronizing.
Solve this by adding a non-blocking mode for ZFS range locks, and using
it in zfs_getpages(). If zfs_getpages() fails to acquire the range
lock, only the fault page will be populated.
Reported by: bdrewery
Reviewed by: avg
Tested by: pho
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D24839
Modified:
head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_rlock.h
head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_rlock.c
head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_rlock.h
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_rlock.h Wed May 20 17:48:18 2020 (r361286)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_rlock.h Wed May 20 18:29:23 2020 (r361287)
@@ -78,6 +78,8 @@ void rangelock_fini(rangelock_t *);
locked_range_t *rangelock_enter(rangelock_t *,
uint64_t, uint64_t, rangelock_type_t);
+locked_range_t *rangelock_tryenter(rangelock_t *,
+ uint64_t, uint64_t, rangelock_type_t);
void rangelock_exit(locked_range_t *);
void rangelock_reduce(locked_range_t *, uint64_t, uint64_t);
Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_rlock.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_rlock.c Wed May 20 17:48:18 2020 (r361286)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_rlock.c Wed May 20 18:29:23 2020 (r361287)
@@ -136,10 +136,11 @@ rangelock_fini(rangelock_t *rl)
}
/*
- * Check if a write lock can be grabbed, or wait and recheck until available.
+ * Check if a write lock can be grabbed. If not, fail immediately or sleep and
+ * recheck until available, depending on the value of the "nonblock" parameter.
*/
-static void
-rangelock_enter_writer(rangelock_t *rl, locked_range_t *new)
+static boolean_t
+rangelock_enter_writer(rangelock_t *rl, locked_range_t *new, boolean_t nonblock)
{
avl_tree_t *tree = &rl->rl_tree;
locked_range_t *lr;
@@ -169,7 +170,7 @@ rangelock_enter_writer(rangelock_t *rl, locked_range_t
*/
if (avl_numnodes(tree) == 0) {
avl_add(tree, new);
- return;
+ return (B_TRUE);
}
/*
@@ -190,8 +191,10 @@ rangelock_enter_writer(rangelock_t *rl, locked_range_t
goto wait;
avl_insert(tree, new, where);
- return;
+ return (B_TRUE);
wait:
+ if (nonblock)
+ return (B_FALSE);
if (!lr->lr_write_wanted) {
cv_init(&lr->lr_write_cv, NULL, CV_DEFAULT, NULL);
lr->lr_write_wanted = B_TRUE;
@@ -373,10 +376,11 @@ rangelock_add_reader(avl_tree_t *tree, locked_range_t
}
/*
- * Check if a reader lock can be grabbed, or wait and recheck until available.
+ * Check if a reader lock can be grabbed. If not, fail immediately or sleep and
+ * recheck until available, depending on the value of the "nonblock" parameter.
*/
-static void
-rangelock_enter_reader(rangelock_t *rl, locked_range_t *new)
+static boolean_t
+rangelock_enter_reader(rangelock_t *rl, locked_range_t *new, boolean_t nonblock)
{
avl_tree_t *tree = &rl->rl_tree;
locked_range_t *prev, *next;
@@ -397,6 +401,8 @@ retry:
*/
if (prev && (off < prev->lr_offset + prev->lr_length)) {
if ((prev->lr_type == RL_WRITER) || (prev->lr_write_wanted)) {
+ if (nonblock)
+ return (B_FALSE);
if (!prev->lr_read_wanted) {
cv_init(&prev->lr_read_cv,
NULL, CV_DEFAULT, NULL);
@@ -421,6 +427,8 @@ retry:
if (off + len <= next->lr_offset)
goto got_lock;
if ((next->lr_type == RL_WRITER) || (next->lr_write_wanted)) {
+ if (nonblock)
+ return (B_FALSE);
if (!next->lr_read_wanted) {
cv_init(&next->lr_read_cv,
NULL, CV_DEFAULT, NULL);
@@ -439,6 +447,7 @@ got_lock:
* locks and bumping ref counts (r_count).
*/
rangelock_add_reader(tree, new, prev, where);
+ return (B_TRUE);
}
/*
@@ -448,13 +457,13 @@ got_lock:
* the range lock structure for later unlocking (or reduce range if the
* entire file is locked as RL_WRITER).
*/
-locked_range_t *
-rangelock_enter(rangelock_t *rl, uint64_t off, uint64_t len,
- rangelock_type_t type)
+static locked_range_t *
+_rangelock_enter(rangelock_t *rl, uint64_t off, uint64_t len,
+ rangelock_type_t type, boolean_t nonblock)
{
ASSERT(type == RL_READER || type == RL_WRITER || type == RL_APPEND);
- locked_range_t *new = kmem_alloc(sizeof (locked_range_t), KM_SLEEP);
+ locked_range_t *new = kmem_alloc(sizeof (*new), KM_SLEEP);
new->lr_rangelock = rl;
new->lr_offset = off;
if (len + off < off) /* overflow */
@@ -471,14 +480,32 @@ rangelock_enter(rangelock_t *rl, uint64_t off, uint64_
/*
* First check for the usual case of no locks
*/
- if (avl_numnodes(&rl->rl_tree) == 0)
+ if (avl_numnodes(&rl->rl_tree) == 0) {
avl_add(&rl->rl_tree, new);
- else
- rangelock_enter_reader(rl, new);
- } else
- rangelock_enter_writer(rl, new); /* RL_WRITER or RL_APPEND */
+ } else if (!rangelock_enter_reader(rl, new, nonblock)) {
+ kmem_free(new, sizeof (*new));
+ new = NULL;
+ }
+ } else if (!rangelock_enter_writer(rl, new, nonblock)) {
+ kmem_free(new, sizeof (*new));
+ new = NULL;
+ }
mutex_exit(&rl->rl_lock);
return (new);
+}
+
+locked_range_t *
+rangelock_enter(rangelock_t *rl, uint64_t off, uint64_t len,
+ rangelock_type_t type)
+{
+ return (_rangelock_enter(rl, off, len, type, B_FALSE));
+}
+
+locked_range_t *
+rangelock_tryenter(rangelock_t *rl, uint64_t off, uint64_t len,
+ rangelock_type_t type)
+{
+ return (_rangelock_enter(rl, off, len, type, B_TRUE));
}
/*
Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c Wed May 20 17:48:18 2020 (r361286)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c Wed May 20 18:29:23 2020 (r361287)
@@ -4498,13 +4498,27 @@ zfs_getpages(struct vnode *vp, vm_page_t *ma, int coun
end = IDX_TO_OFF(ma[count - 1]->pindex + 1);
/*
- * Lock a range covering all required and optional pages.
- * Note that we need to handle the case of the block size growing.
+ * Try to lock a range covering all required and optional pages, to
+ * handle the case of the block size growing. It is not safe to block
+ * on the range lock since the owner may be waiting for the fault page
+ * to be unbusied.
*/
for (;;) {
blksz = zp->z_blksz;
- lr = rangelock_enter(&zp->z_rangelock, rounddown(start, blksz),
+ lr = rangelock_tryenter(&zp->z_rangelock,
+ rounddown(start, blksz),
roundup(end, blksz) - rounddown(start, blksz), RL_READER);
+ if (lr == NULL) {
+ if (rahead != NULL) {
+ *rahead = 0;
+ rahead = NULL;
+ }
+ if (rbehind != NULL) {
+ *rbehind = 0;
+ rbehind = NULL;
+ }
+ break;
+ }
if (blksz == zp->z_blksz)
break;
rangelock_exit(lr);
@@ -4515,7 +4529,8 @@ zfs_getpages(struct vnode *vp, vm_page_t *ma, int coun
obj_size = object->un_pager.vnp.vnp_size;
zfs_vmobject_wunlock(object);
if (IDX_TO_OFF(ma[count - 1]->pindex) >= obj_size) {
- rangelock_exit(lr);
+ if (lr != NULL)
+ rangelock_exit(lr);
ZFS_EXIT(zfsvfs);
return (zfs_vm_pagerret_bad);
}
@@ -4543,7 +4558,8 @@ zfs_getpages(struct vnode *vp, vm_page_t *ma, int coun
error = dmu_read_pages(os, zp->z_id, ma, count, &pgsin_b, &pgsin_a,
MIN(end, obj_size) - (end - PAGE_SIZE));
- rangelock_exit(lr);
+ if (lr != NULL)
+ rangelock_exit(lr);
ZFS_ACCESSTIME_STAMP(zfsvfs, zp);
ZFS_EXIT(zfsvfs);
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