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?
>> 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.
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
>>
>
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