Hello Junxiao,
>From the initial description, the second lock_XYZ(PR) should be blocked, since
>DLM have a fair queue mechanism, otherwise, it looks to bring a write lock
>starvation.
Second, this issue can be reproduced in old Linux kernels (e.g. 3.16.7-24)?
there should not be any regression issue?
Finally, really do not like nested using lock, can we avoid this.
Thanks
Gang
--
<The HTML signature 'New Signature' does not contain any text>
>>>
> 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...@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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> Ocfs2-devel@oss.oracle.com
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