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Implement a proper rw_tryupgrade

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Current rw_tryupgrade does rw_exit and then rw_tryenter(RW_RWITER), and then
does rw_enter(RW_READER) if it fails. This violate the assumption that
rw_tryupgrade should be atomic and could cause extra contention or even lock
inversion.

This patch we implement a proper rw_tryupgrade. For rwsem-spinlock, we take
the spinlock to check rwsem->count and rwsem->wait_list. For normal rwsem, we
use cmpxchg on rwsem->count to change the value from single reader to single
writer.

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes zfsonlinux/zfs#4692
Closes #554
This commit is contained in:
Chunwei Chen
2016-05-25 16:35:42 -07:00
committed by Brian Behlendorf
parent c60a51b640
commit f58040c0fc
5 changed files with 147 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/splat/splat-rwlock.c
+60 -6
View File
@@ -55,8 +55,12 @@
#define SPLAT_RWLOCK_TEST5_DESC "Write downgrade"
#define SPLAT_RWLOCK_TEST6_ID 0x0706
#define SPLAT_RWLOCK_TEST6_NAME "rw_tryupgrade"
#define SPLAT_RWLOCK_TEST6_DESC "Read upgrade"
#define SPLAT_RWLOCK_TEST6_NAME "rw_tryupgrade-1"
#define SPLAT_RWLOCK_TEST6_DESC "rwsem->count value"
#define SPLAT_RWLOCK_TEST7_ID 0x0707
#define SPLAT_RWLOCK_TEST7_NAME "rw_tryupgrade-2"
#define SPLAT_RWLOCK_TEST7_DESC "Read upgrade"
#define SPLAT_RWLOCK_TEST_MAGIC 0x115599DDUL
#define SPLAT_RWLOCK_TEST_NAME "rwlock_test"
@@ -580,8 +584,55 @@ splat_rwlock_test6(struct file *file, void *arg)
splat_init_rw_priv(rwp, file);
rw_enter(&rwp->rw_rwlock, RW_READER);
if (!RW_READ_HELD(&rwp->rw_rwlock)) {
if (RWSEM_COUNT(SEM(&rwp->rw_rwlock)) !=
SPL_RWSEM_SINGLE_READER_VALUE) {
splat_vprint(file, SPLAT_RWLOCK_TEST6_NAME,
"We assumed single reader rwsem->count "
"should be %ld, but is %ld\n",
SPL_RWSEM_SINGLE_READER_VALUE,
RWSEM_COUNT(SEM(&rwp->rw_rwlock)));
rc = -ENOLCK;
goto out;
}
rw_exit(&rwp->rw_rwlock);
rw_enter(&rwp->rw_rwlock, RW_WRITER);
if (RWSEM_COUNT(SEM(&rwp->rw_rwlock)) !=
SPL_RWSEM_SINGLE_WRITER_VALUE) {
splat_vprint(file, SPLAT_RWLOCK_TEST6_NAME,
"We assumed single writer rwsem->count "
"should be %ld, but is %ld\n",
SPL_RWSEM_SINGLE_WRITER_VALUE,
RWSEM_COUNT(SEM(&rwp->rw_rwlock)));
rc = -ENOLCK;
goto out;
}
rc = 0;
splat_vprint(file, SPLAT_RWLOCK_TEST6_NAME, "%s",
"rwsem->count same as we assumed\n");
out:
rw_exit(&rwp->rw_rwlock);
rw_destroy(&rwp->rw_rwlock);
kfree(rwp);
return rc;
}
static int
splat_rwlock_test7(struct file *file, void *arg)
{
rw_priv_t *rwp;
int rc;
rwp = (rw_priv_t *)kmalloc(sizeof(*rwp), GFP_KERNEL);
if (rwp == NULL)
return -ENOMEM;
splat_init_rw_priv(rwp, file);
rw_enter(&rwp->rw_rwlock, RW_READER);
if (!RW_READ_HELD(&rwp->rw_rwlock)) {
splat_vprint(file, SPLAT_RWLOCK_TEST7_NAME,
"rwlock should be read lock: %d\n",
RW_READ_HELD(&rwp->rw_rwlock));
rc = -ENOLCK;
@@ -591,7 +642,7 @@ splat_rwlock_test6(struct file *file, void *arg)
/* With one reader upgrade should never fail. */
rc = rw_tryupgrade(&rwp->rw_rwlock);
if (!rc) {
splat_vprint(file, SPLAT_RWLOCK_TEST6_NAME,
splat_vprint(file, SPLAT_RWLOCK_TEST7_NAME,
"rwlock failed upgrade from reader: %d\n",
RW_READ_HELD(&rwp->rw_rwlock));
rc = -ENOLCK;
@@ -599,7 +650,7 @@ splat_rwlock_test6(struct file *file, void *arg)
}
if (RW_READ_HELD(&rwp->rw_rwlock) || !RW_WRITE_HELD(&rwp->rw_rwlock)) {
splat_vprint(file, SPLAT_RWLOCK_TEST6_NAME, "rwlock should "
splat_vprint(file, SPLAT_RWLOCK_TEST7_NAME, "rwlock should "
"have 0 (not %d) reader and 1 (not %d) writer\n",
RW_READ_HELD(&rwp->rw_rwlock),
RW_WRITE_HELD(&rwp->rw_rwlock));
@@ -607,7 +658,7 @@ splat_rwlock_test6(struct file *file, void *arg)
}
rc = 0;
splat_vprint(file, SPLAT_RWLOCK_TEST6_NAME, "%s",
splat_vprint(file, SPLAT_RWLOCK_TEST7_NAME, "%s",
"rwlock properly upgraded\n");
out:
rw_exit(&rwp->rw_rwlock);
@@ -646,6 +697,8 @@ splat_rwlock_init(void)
SPLAT_RWLOCK_TEST5_ID, splat_rwlock_test5);
SPLAT_TEST_INIT(sub, SPLAT_RWLOCK_TEST6_NAME, SPLAT_RWLOCK_TEST6_DESC,
SPLAT_RWLOCK_TEST6_ID, splat_rwlock_test6);
SPLAT_TEST_INIT(sub, SPLAT_RWLOCK_TEST7_NAME, SPLAT_RWLOCK_TEST7_DESC,
SPLAT_RWLOCK_TEST7_ID, splat_rwlock_test7);
return sub;
}
@@ -654,6 +707,7 @@ void
splat_rwlock_fini(splat_subsystem_t *sub)
{
ASSERT(sub);
SPLAT_TEST_FINI(sub, SPLAT_RWLOCK_TEST7_ID);
SPLAT_TEST_FINI(sub, SPLAT_RWLOCK_TEST6_ID);
SPLAT_TEST_FINI(sub, SPLAT_RWLOCK_TEST5_ID);
SPLAT_TEST_FINI(sub, SPLAT_RWLOCK_TEST4_ID);