Hi,
On Mon, Dec 14, 2015 at 05:02:26PM +0800, Junxiao Bi wrote:
> On 12/14/2015 04:44 PM, Eric Ren wrote:
> > Hi Junxiao,
> >
> > On Mon, Dec 14, 2015 at 09:57:38AM +0800, Junxiao Bi wrote:
> >> 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
> > Recording process hurts scalability, performace and readability heavily,
> > right?
> Do you mean searching the l_owner_list of lockres when locking hurting
> the above?
Hm, yes.
>
> >> can fix PR+PR, EX+EX, EX+PR deadlock. But it can't fix the PR+EX deadlock,
> > Could you please describe why PR+EX is special?
> Because on the master nodes, the lockres of blocked node Y is in the
> position before the one of node X from the converting list. So even let
> Ex go from Node X, still a deadlock.
Got it, thanks.
Eric
>
> Thanks,
> Junxiao.
>
> >
> > Thanks,
> > Eric
> >> 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
> >>
> >>
> >> _______________________________________________
> >> Ocfs2-devel mailing list
> >> Ocfs2-devel@oss.oracle.com
> >> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
> >>
> >
> > _______________________________________________
> > Ocfs2-devel mailing list
> > Ocfs2-devel@oss.oracle.com
> > https://oss.oracle.com/mailman/listinfo/ocfs2-devel
> >
>
>
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