[Ocfs2-devel] [PATCH] ocfs2: dlm: fix recursive locking deadlock
Junxiao Bi
junxiao.bi at oracle.com
Sun Dec 13 17:57:38 PST 2015
The following locking order can cause a deadlock.
Process A on Node X: Process B on Node Y:
lock_XYZ(PR)
lock_XYZ(EX)
lock_XYZ(PR) >>> blocked forever by OCFS2_LOCK_BLOCKED.
Use ocfs2-test multiple reflink test can reproduce this on v4.3 kernel,
the whole cluster hung, and get the following call trace.
INFO: task multi_reflink_t:10118 blocked for more than 120 seconds.
Tainted: G OE 4.3.0 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
multi_reflink_t D ffff88003e816980 0 10118 10117 0x00000080
ffff880005b735f8 0000000000000082 ffffffff81a25500 ffff88003e750000
ffff880005b735c8 ffffffff8117992f ffffea0000929f80 ffff88003e816980
7fffffffffffffff 0000000000000000 0000000000000001 ffffea0000929f80
Call Trace:
[<ffffffff8117992f>] ? find_get_entry+0x2f/0xc0
[<ffffffff816a68fe>] schedule+0x3e/0x80
[<ffffffff816a9358>] schedule_timeout+0x1c8/0x220
[<ffffffffa067eee4>] ? ocfs2_inode_cache_unlock+0x14/0x20 [ocfs2]
[<ffffffffa06bb1e9>] ? ocfs2_metadata_cache_unlock+0x19/0x30 [ocfs2]
[<ffffffffa06bb399>] ? ocfs2_buffer_cached+0x99/0x170 [ocfs2]
[<ffffffffa067eee4>] ? ocfs2_inode_cache_unlock+0x14/0x20 [ocfs2]
[<ffffffffa06bb1e9>] ? ocfs2_metadata_cache_unlock+0x19/0x30 [ocfs2]
[<ffffffff810c5f41>] ? __raw_callee_save___pv_queued_spin_unlock+0x11/0x20
[<ffffffff816a78ae>] wait_for_completion+0xde/0x110
[<ffffffff810a81b0>] ? try_to_wake_up+0x240/0x240
[<ffffffffa066f65d>] __ocfs2_cluster_lock+0x20d/0x720 [ocfs2]
[<ffffffff810c5f41>] ? __raw_callee_save___pv_queued_spin_unlock+0x11/0x20
[<ffffffffa0674841>] ocfs2_inode_lock_full_nested+0x181/0x400 [ocfs2]
[<ffffffffa06d0db3>] ? ocfs2_iop_get_acl+0x53/0x113 [ocfs2]
[<ffffffff81210cd2>] ? igrab+0x42/0x70
[<ffffffffa06d0db3>] ocfs2_iop_get_acl+0x53/0x113 [ocfs2]
[<ffffffff81254583>] get_acl+0x53/0x70
[<ffffffff81254923>] posix_acl_create+0x73/0x130
[<ffffffffa068f0bf>] ocfs2_mknod+0x7cf/0x1140 [ocfs2]
[<ffffffffa068fba2>] ocfs2_create+0x62/0x110 [ocfs2]
[<ffffffff8120be25>] ? __d_alloc+0x65/0x190
[<ffffffff81201b3e>] ? __inode_permission+0x4e/0xd0
[<ffffffff81202cf5>] vfs_create+0xd5/0x100
[<ffffffff812009ed>] ? lookup_real+0x1d/0x60
[<ffffffff81203a03>] lookup_open+0x173/0x1a0
[<ffffffff810c59c6>] ? percpu_down_read+0x16/0x70
[<ffffffff81205fea>] do_last+0x31a/0x830
[<ffffffff81201b3e>] ? __inode_permission+0x4e/0xd0
[<ffffffff81201bd8>] ? inode_permission+0x18/0x50
[<ffffffff812046b0>] ? link_path_walk+0x290/0x550
[<ffffffff8120657c>] path_openat+0x7c/0x140
[<ffffffff812066c5>] do_filp_open+0x85/0xe0
[<ffffffff8120190f>] ? getname_flags+0x7f/0x1f0
[<ffffffff811f613a>] do_sys_open+0x11a/0x220
[<ffffffff8100374b>] ? syscall_trace_enter_phase1+0x15b/0x170
[<ffffffff811f627e>] SyS_open+0x1e/0x20
[<ffffffff816aa2ae>] entry_SYSCALL_64_fastpath+0x12/0x71
commit 743b5f1434f5 ("ocfs2: take inode lock in ocfs2_iop_set/get_acl()")
add a recursive locking to ocfs2_mknod() which exports this deadlock, but
indeed this is a common issue, it can be triggered in other place.
Record processes who owned the cluster lock, allow recursive lock to go
can fix PR+PR, EX+EX, EX+PR deadlock. But it can't fix the PR+EX deadlock,
to avoid this, the second EX locking must use non-block way.
Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
---
fs/ocfs2/dlmglue.c | 209 ++++++++++++++++++++++++++++++++++++++++++++++++----
fs/ocfs2/ocfs2.h | 15 ++++
2 files changed, 211 insertions(+), 13 deletions(-)
diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 1c91103..e46be46 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -33,6 +33,7 @@
#include <linux/seq_file.h>
#include <linux/time.h>
#include <linux/quotaops.h>
+#include <linux/delay.h>
#define MLOG_MASK_PREFIX ML_DLM_GLUE
#include <cluster/masklog.h>
@@ -115,6 +116,7 @@ static int ocfs2_check_refcount_downconvert(struct ocfs2_lock_res *lockres,
int new_level);
static int ocfs2_refcount_convert_worker(struct ocfs2_lock_res *lockres,
int blocking);
+static int ocfs2_is_recursive_lock(struct ocfs2_lock_res *lockres);
#define mlog_meta_lvb(__level, __lockres) ocfs2_dump_meta_lvb_info(__level, __PRETTY_FUNCTION__, __LINE__, __lockres)
@@ -341,8 +343,9 @@ static int ocfs2_lock_create(struct ocfs2_super *osb,
struct ocfs2_lock_res *lockres,
int level,
u32 dlm_flags);
-static inline int ocfs2_may_continue_on_blocked_lock(struct ocfs2_lock_res *lockres,
- int wanted);
+static inline int
+ocfs2_may_continue_on_blocked_lock(struct ocfs2_lock_res *lockres,
+ int wanted, int nonblock, int *canwait);
static void __ocfs2_cluster_unlock(struct ocfs2_super *osb,
struct ocfs2_lock_res *lockres,
int level, unsigned long caller_ip);
@@ -531,6 +534,7 @@ void ocfs2_lock_res_init_once(struct ocfs2_lock_res *res)
init_waitqueue_head(&res->l_event);
INIT_LIST_HEAD(&res->l_blocked_list);
INIT_LIST_HEAD(&res->l_mask_waiters);
+ INIT_LIST_HEAD(&res->l_owner_list);
}
void ocfs2_inode_lock_res_init(struct ocfs2_lock_res *res,
@@ -782,6 +786,10 @@ static inline void ocfs2_dec_holders(struct ocfs2_lock_res *lockres,
default:
BUG();
}
+
+ /* l_owner_list should be empty if no holders. */
+ BUG_ON(!lockres->l_ex_holders && !lockres->l_ro_holders \
+ && !list_empty(&lockres->l_owner_list));
}
/* WARNING: This function lives in a world where the only three lock
@@ -1287,15 +1295,37 @@ static inline void ocfs2_wait_on_refreshing_lock(struct ocfs2_lock_res *lockres)
!ocfs2_check_wait_flag(lockres, OCFS2_LOCK_REFRESHING));
}
-/* predict what lock level we'll be dropping down to on behalf
- * of another node, and return true if the currently wanted
- * level will be compatible with it. */
-static inline int ocfs2_may_continue_on_blocked_lock(struct ocfs2_lock_res *lockres,
- int wanted)
+/* If wanted level is compatible with blocked one, then allow it go.
+ * To avoid deadlock, recursive locking should be let go. An exception
+ * is block asking for PR+EX recursive lock, it is not supported, the
+ * second EX locking should use nonblock way, or will cause deadlock.
+ */
+static inline int
+ocfs2_may_continue_on_blocked_lock(struct ocfs2_lock_res *lockres,
+ int wanted, int nonblock, int *canwait)
{
BUG_ON(!(lockres->l_flags & OCFS2_LOCK_BLOCKED));
- return wanted <= ocfs2_highest_compat_lock_level(lockres->l_blocking);
+ *canwait = 1;
+ if (wanted <= ocfs2_highest_compat_lock_level(lockres->l_blocking))
+ return 1;
+
+ /* non-recursive lock not allowed to go to avoid possible
+ * starvation of blocked node.
+ */
+ if (!ocfs2_is_recursive_lock(lockres))
+ return 0;
+
+ /* block asking for PR+EX recursive lock not allowed. */
+ if (lockres->l_level == DLM_LOCK_PR && wanted == DLM_LOCK_EX
+ && !nonblock) {
+ *canwait = 0;
+ mlog(ML_ERROR, "block asking for PR+EX recursive lock not allowed.\n");
+ return 0;
+
+ }
+
+ return 1;
}
static void ocfs2_init_mask_waiter(struct ocfs2_mask_waiter *mw)
@@ -1375,6 +1405,131 @@ static int ocfs2_wait_for_mask_interruptible(struct ocfs2_mask_waiter *mw,
return ret;
}
+static struct ocfs2_pid_locking *ocfs2_alloc_pid_locking(void)
+{
+ struct ocfs2_pid_locking *pid_locking;
+
+retry:
+ pid_locking = kmalloc(sizeof(struct ocfs2_pid_locking), GFP_NOFS);
+ if (!pid_locking) {
+ msleep(100);
+ goto retry;
+ }
+
+ INIT_LIST_HEAD(&pid_locking->next);
+ pid_locking->ro_holders = 0;
+ pid_locking->ex_holders = 0;
+ pid_locking->pid = current->pid;
+
+ return pid_locking;
+}
+
+static void ocfs2_free_pid_locking(struct ocfs2_pid_locking *pid_locking)
+{
+ list_del(&pid_locking->next);
+ kfree(pid_locking);
+}
+
+static struct ocfs2_pid_locking *
+ocfs2_find_pid_locking(struct ocfs2_lock_res *lockres)
+{
+ struct ocfs2_pid_locking *pid_locking;
+
+ list_for_each_entry(pid_locking, &lockres->l_owner_list, next) {
+ if (pid_locking->pid == current->pid)
+ return pid_locking;
+ }
+
+ return NULL;
+}
+
+static void
+ocfs2_pid_locking_update_holder(struct ocfs2_pid_locking *pid_locking,
+ int level, int lock)
+{
+ if (level == DLM_LOCK_EX) {
+ if (lock)
+ pid_locking->ex_holders++;
+ else
+ pid_locking->ex_holders--;
+ } else if (level == DLM_LOCK_PR) {
+ if (lock)
+ pid_locking->ro_holders++;
+ else
+ pid_locking->ro_holders--;
+ } else
+ BUG();
+}
+
+static void ocfs2_pid_locking_update(struct ocfs2_lock_res *lockres,
+ struct ocfs2_pid_locking *pid_locking, int level, int lock)
+{
+ /* new alloced pid_locking linked to l_owner_list. */
+ if (!pid_locking->ro_holders && !pid_locking->ex_holders)
+ list_add_tail(&pid_locking->next, &lockres->l_owner_list);
+
+ ocfs2_pid_locking_update_holder(pid_locking, level, lock);
+}
+
+static void ocfs2_get_pid_locking(struct ocfs2_lock_res *lockres,
+ struct ocfs2_pid_locking *pid_locking, int level)
+{
+ ocfs2_pid_locking_update(lockres, pid_locking, level, 1);
+}
+
+static void ocfs2_put_pid_locking(struct ocfs2_lock_res *lockres,
+ struct ocfs2_pid_locking *pid_locking, int level)
+{
+ struct ocfs2_pid_locking *plocking, *next;
+ struct list_head *head = &lockres->l_owner_list;
+ int total_ro_holders = 0, total_ex_holders = 0;
+
+ ocfs2_pid_locking_update(lockres, pid_locking, level, 0);
+
+ /* free unused pid locking. */
+ if (!pid_locking->ro_holders && !pid_locking->ex_holders) {
+ ocfs2_free_pid_locking(pid_locking);
+ return;
+ }
+
+ /* If get here, it means lock/unlock happened in different processes,
+ * or a bug where unlock happened without lock first. Let check.
+ */
+ list_for_each_entry(plocking, head, next) {
+ total_ro_holders += plocking->ro_holders;
+ total_ex_holders += plocking->ex_holders;
+ }
+
+ /* locked and unlocked in different processs, the lock is not hold now,
+ * free all pid_locking entries.
+ */
+ if (!total_ro_holders && !total_ex_holders) {
+ list_for_each_entry_safe(plocking, next, head, next) {
+ ocfs2_free_pid_locking(plocking);
+ }
+ } else if (total_ro_holders < 0 || total_ex_holders < 0) {
+ mlog(ML_ERROR, "lockres %s unlocked but not locked first.\n",
+ lockres->l_name);
+ BUG();
+ }
+}
+
+/* lock at least twice before unlock in one process is recursive locking. */
+static int ocfs2_is_recursive_lock(struct ocfs2_lock_res *lockres)
+{
+ struct ocfs2_pid_locking *pid_locking;
+
+ list_for_each_entry(pid_locking, &lockres->l_owner_list, next) {
+ if (pid_locking->pid != current->pid)
+ continue;
+
+ return (pid_locking->ro_holders > 0 ||
+ pid_locking->ex_holders > 0);
+ }
+
+ return 0;
+}
+
static int __ocfs2_cluster_lock(struct ocfs2_super *osb,
struct ocfs2_lock_res *lockres,
int level,
@@ -1390,6 +1545,9 @@ static int __ocfs2_cluster_lock(struct ocfs2_super *osb,
unsigned int gen;
int noqueue_attempted = 0;
int dlm_locked = 0;
+ struct ocfs2_pid_locking *pid_locking = NULL;
+ int canwait = 1;
+ int nonblock = arg_flags & OCFS2_LOCK_NONBLOCK;
if (!(lockres->l_flags & OCFS2_LOCK_INITIALIZED)) {
mlog_errno(-EINVAL);
@@ -1405,6 +1563,14 @@ again:
wait = 0;
spin_lock_irqsave(&lockres->l_lock, flags);
+ if (!pid_locking) {
+ pid_locking = ocfs2_find_pid_locking(lockres);
+ if (!pid_locking) {
+ spin_unlock_irqrestore(&lockres->l_lock, flags);
+ pid_locking = ocfs2_alloc_pid_locking();
+ spin_lock_irqsave(&lockres->l_lock, flags);
+ }
+ }
if (catch_signals && signal_pending(current)) {
ret = -ERESTARTSYS;
@@ -1447,7 +1613,8 @@ again:
}
if (lockres->l_flags & OCFS2_LOCK_BLOCKED &&
- !ocfs2_may_continue_on_blocked_lock(lockres, level)) {
+ !ocfs2_may_continue_on_blocked_lock(lockres, level,
+ nonblock, &canwait)) {
/* is the lock is currently blocked on behalf of
* another node */
lockres_add_mask_waiter(lockres, &mw, OCFS2_LOCK_BLOCKED, 0);
@@ -1519,6 +1686,7 @@ again:
update_holders:
/* Ok, if we get here then we're good to go. */
ocfs2_inc_holders(lockres, level);
+ ocfs2_get_pid_locking(lockres, pid_locking, level);
ret = 0;
unlock:
@@ -1534,7 +1702,7 @@ out:
* This block is helping an aop path notice the inversion and back
* off to unlock its page lock before trying the dlm lock again.
*/
- if (wait && arg_flags & OCFS2_LOCK_NONBLOCK &&
+ if (wait && nonblock &&
mw.mw_mask & (OCFS2_LOCK_BUSY|OCFS2_LOCK_BLOCKED)) {
wait = 0;
spin_lock_irqsave(&lockres->l_lock, flags);
@@ -1550,9 +1718,12 @@ out:
}
}
if (wait) {
- ret = ocfs2_wait_for_mask(&mw);
- if (ret == 0)
- goto again;
+ if (canwait) {
+ ret = ocfs2_wait_for_mask(&mw);
+ if (ret == 0)
+ goto again;
+ } else
+ ret = -EPERM;
mlog_errno(ret);
}
ocfs2_update_lock_stats(lockres, level, &mw, ret);
@@ -1569,6 +1740,10 @@ out:
caller_ip);
}
#endif
+ /* free unused pid_locking if error. */
+ if (ret && !pid_locking->ro_holders && !pid_locking->ex_holders)
+ ocfs2_free_pid_locking(pid_locking);
+
return ret;
}
@@ -1589,8 +1764,16 @@ static void __ocfs2_cluster_unlock(struct ocfs2_super *osb,
unsigned long caller_ip)
{
unsigned long flags;
+ struct ocfs2_pid_locking *pid_locking;
spin_lock_irqsave(&lockres->l_lock, flags);
+ pid_locking = ocfs2_find_pid_locking(lockres);
+ if (!pid_locking) {
+ spin_unlock_irqrestore(&lockres->l_lock, flags);
+ pid_locking = ocfs2_alloc_pid_locking();
+ spin_lock_irqsave(&lockres->l_lock, flags);
+ }
+ ocfs2_put_pid_locking(lockres, pid_locking, level);
ocfs2_dec_holders(lockres, level);
ocfs2_downconvert_on_unlock(osb, lockres);
spin_unlock_irqrestore(&lockres->l_lock, flags);
diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
index 7a01262..bf80fb7 100644
--- a/fs/ocfs2/ocfs2.h
+++ b/fs/ocfs2/ocfs2.h
@@ -165,6 +165,19 @@ struct ocfs2_lock_stats {
};
#endif
+/* locking stat of processes. */
+struct ocfs2_pid_locking {
+ /* used to link into lockres->l_owner_list. */
+ struct list_head next;
+ /* inc by 1 when lock PR and dec by 1 when unlock PR. It could be
+ * negative number if lock/unlock happened in different processes.
+ */
+ int ro_holders;
+ int ex_holders;
+ /* the process who is using this lock. */
+ pid_t pid;
+};
+
struct ocfs2_lock_res {
void *l_priv;
struct ocfs2_lock_res_ops *l_ops;
@@ -207,6 +220,8 @@ struct ocfs2_lock_res {
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map l_lockdep_map;
#endif
+ /* save all processes who owned this lock. */
+ struct list_head l_owner_list;
};
enum ocfs2_orphan_reco_type {
--
1.7.9.5
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