From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750933AbdAQIvl (ORCPT ); Tue, 17 Jan 2017 03:51:41 -0500 Received: from mail-oi0-f66.google.com ([209.85.218.66]:34187 "EHLO mail-oi0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750782AbdAQIvj (ORCPT ); Tue, 17 Jan 2017 03:51:39 -0500 Subject: Re: [PATCH v3 1/2] ocfs2/dlmglue: prepare tracking logic to avoid recursive cluster lock To: Eric Ren , ocfs2-devel@oss.oracle.com References: <20170117063054.30519-1-zren@suse.com> <20170117063054.30519-2-zren@suse.com> <32cc4980-baa2-8b58-129d-8c7abc11cb87@gmail.com> <2d740f33-825d-bd32-a6bc-68ded55ab621@suse.com> Cc: akpm@linux-foundation.org, mfasheh@versity.com, jlbec@evilplan.org, ghe@suse.com, junxiao.bi@oracle.com, sfr@canb.auug.org.au, hch@lst.de, linux-kernel@vger.kernel.org From: Joseph Qi Message-ID: <8773427e-34d4-7880-e027-4e9330f73a3a@gmail.com> Date: Tue, 17 Jan 2017 16:43:00 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 MIME-Version: 1.0 In-Reply-To: <2d740f33-825d-bd32-a6bc-68ded55ab621@suse.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/1/17 15:55, Eric Ren wrote: > Hi! > > On 01/17/2017 03:39 PM, Joseph Qi wrote: >> >> On 17/1/17 14:30, Eric Ren wrote: >>> We are in the situation that we have to avoid recursive cluster >>> locking, >>> but there is no way to check if a cluster lock has been taken by a >>> precess already. >>> >>> Mostly, we can avoid recursive locking by writing code carefully. >>> However, we found that it's very hard to handle the routines that >>> are invoked directly by vfs code. For instance: >>> >>> const struct inode_operations ocfs2_file_iops = { >>> .permission = ocfs2_permission, >>> .get_acl = ocfs2_iop_get_acl, >>> .set_acl = ocfs2_iop_set_acl, >>> }; >>> >>> Both ocfs2_permission() and ocfs2_iop_get_acl() call >>> ocfs2_inode_lock(PR): >>> do_sys_open >>> may_open >>> inode_permission >>> ocfs2_permission >>> ocfs2_inode_lock() <=== first time >>> generic_permission >>> get_acl >>> ocfs2_iop_get_acl >>> ocfs2_inode_lock() <=== recursive one >>> >>> A deadlock will occur if a remote EX request comes in between two >>> of ocfs2_inode_lock(). Briefly describe how the deadlock is formed: >>> >>> On one hand, OCFS2_LOCK_BLOCKED flag of this lockres is set in >>> BAST(ocfs2_generic_handle_bast) when downconvert is started >>> on behalf of the remote EX lock request. Another hand, the recursive >>> cluster lock (the second one) will be blocked in in >>> __ocfs2_cluster_lock() >>> because of OCFS2_LOCK_BLOCKED. But, the downconvert never complete, >>> why? >>> because there is no chance for the first cluster lock on this node >>> to be >>> unlocked - we block ourselves in the code path. >>> >>> The idea to fix this issue is mostly taken from gfs2 code. >>> 1. introduce a new field: struct ocfs2_lock_res.l_holders, to >>> keep track of the processes' pid who has taken the cluster lock >>> of this lock resource; >>> 2. introduce a new flag for ocfs2_inode_lock_full: >>> OCFS2_META_LOCK_GETBH; >>> it means just getting back disk inode bh for us if we've got cluster >>> lock. >>> 3. export a helper: ocfs2_is_locked_by_me() is used to check if we >>> have got the cluster lock in the upper code path. >>> >>> The tracking logic should be used by some of the ocfs2 vfs's callbacks, >>> to solve the recursive locking issue cuased by the fact that vfs >>> routines >>> can call into each other. >>> >>> The performance penalty of processing the holder list should only be >>> seen >>> at a few cases where the tracking logic is used, such as get/set acl. >>> >>> You may ask what if the first time we got a PR lock, and the second >>> time >>> we want a EX lock? fortunately, this case never happens in the real >>> world, >>> as far as I can see, including permission check, >>> (get|set)_(acl|attr), and >>> the gfs2 code also do so. >>> >>> Changes since v1: >>> - Let ocfs2_is_locked_by_me() just return true/false to indicate if the >>> process gets the cluster lock - suggested by: Joseph Qi >>> >>> and Junxiao Bi . >>> >>> - Change "struct ocfs2_holder" to a more meaningful name >>> "ocfs2_lock_holder", >>> suggested by: Junxiao Bi. >>> >>> - Do not inline functions whose bodies are not in scope, changed by: >>> Stephen Rothwell . >>> >>> Changes since v2: >>> - Wrap the tracking logic code of recursive locking into functions, >>> ocfs2_inode_lock_tracker() and ocfs2_inode_unlock_tracker(), >>> suggested by: Junxiao Bi. >>> >>> [sfr@canb.auug.org.au remove some inlines] >>> Signed-off-by: Eric Ren >>> --- >>> fs/ocfs2/dlmglue.c | 105 >>> +++++++++++++++++++++++++++++++++++++++++++++++++++-- >>> fs/ocfs2/dlmglue.h | 18 +++++++++ >>> fs/ocfs2/ocfs2.h | 1 + >>> 3 files changed, 121 insertions(+), 3 deletions(-) >>> >>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c >>> index 77d1632..c75b9e9 100644 >>> --- a/fs/ocfs2/dlmglue.c >>> +++ b/fs/ocfs2/dlmglue.c >>> @@ -532,6 +532,7 @@ 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_holders); >>> } >>> void ocfs2_inode_lock_res_init(struct ocfs2_lock_res *res, >>> @@ -749,6 +750,50 @@ void ocfs2_lock_res_free(struct ocfs2_lock_res >>> *res) >>> res->l_flags = 0UL; >>> } >>> +/* >>> + * Keep a list of processes who have interest in a lockres. >>> + * Note: this is now only uesed for check recursive cluster locking. >>> + */ >>> +static inline void ocfs2_add_holder(struct ocfs2_lock_res *lockres, >>> + struct ocfs2_lock_holder *oh) >>> +{ >>> + INIT_LIST_HEAD(&oh->oh_list); >>> + oh->oh_owner_pid = get_pid(task_pid(current)); >> Trim the redundant space here. > > You mean the blank line here? If so, I am OK to make the change. But, > I'm little worried about people may feel annoyed if I send the v4 > patch set, > hah. > oh->oh_owner_pid = get_pid(task_pid(current)); ^ Here you put one more space. You can check your patches using checkpatch.pl then decide if need send a new version. Thanks, Joseph >> Others look good to me. >> Reviewed-by: Joseph Qi > > Thanks for your guys' review! > Eric >>> + >>> + spin_lock(&lockres->l_lock); >>> + list_add_tail(&oh->oh_list, &lockres->l_holders); >>> + spin_unlock(&lockres->l_lock); >>> +} >>> + >>> +static inline void ocfs2_remove_holder(struct ocfs2_lock_res *lockres, >>> + struct ocfs2_lock_holder *oh) >>> +{ >>> + spin_lock(&lockres->l_lock); >>> + list_del(&oh->oh_list); >>> + spin_unlock(&lockres->l_lock); >>> + >>> + put_pid(oh->oh_owner_pid); >>> +} >>> + >>> +static inline int ocfs2_is_locked_by_me(struct ocfs2_lock_res >>> *lockres) >>> +{ >>> + struct ocfs2_lock_holder *oh; >>> + struct pid *pid; >>> + >>> + /* look in the list of holders for one with the current task as >>> owner */ >>> + spin_lock(&lockres->l_lock); >>> + pid = task_pid(current); >>> + list_for_each_entry(oh, &lockres->l_holders, oh_list) { >>> + if (oh->oh_owner_pid == pid) { >>> + spin_unlock(&lockres->l_lock); >>> + return 1; >>> + } >>> + } >>> + spin_unlock(&lockres->l_lock); >>> + >>> + return 0; >>> +} >>> + >>> static inline void ocfs2_inc_holders(struct ocfs2_lock_res *lockres, >>> int level) >>> { >>> @@ -2333,8 +2378,9 @@ int ocfs2_inode_lock_full_nested(struct inode >>> *inode, >>> goto getbh; >>> } >>> - if (ocfs2_mount_local(osb)) >>> - goto local; >>> + if ((arg_flags & OCFS2_META_LOCK_GETBH) || >>> + ocfs2_mount_local(osb)) >>> + goto update; >>> if (!(arg_flags & OCFS2_META_LOCK_RECOVERY)) >>> ocfs2_wait_for_recovery(osb); >>> @@ -2363,7 +2409,7 @@ int ocfs2_inode_lock_full_nested(struct inode >>> *inode, >>> if (!(arg_flags & OCFS2_META_LOCK_RECOVERY)) >>> ocfs2_wait_for_recovery(osb); >>> -local: >>> +update: >>> /* >>> * We only see this flag if we're being called from >>> * ocfs2_read_locked_inode(). It means we're locking an inode >>> @@ -2497,6 +2543,59 @@ void ocfs2_inode_unlock(struct inode *inode, >>> ocfs2_cluster_unlock(OCFS2_SB(inode->i_sb), lockres, level); >>> } >>> +/* >>> + * This _tracker variantes are introduced to deal with the >>> recursive cluster >>> + * locking issue. The idea is to keep track of a lock holder on the >>> stack of >>> + * the current process. If there's a lock holder on the stack, we >>> know the >>> + * task context is already protected by cluster locking. Currently, >>> they're >>> + * used in some VFS entry routines. >>> + * >>> + * return < 0 on error, return == 0 if there's no lock holder on >>> the stack >>> + * before this call, return == 1 if this call would be a recursive >>> locking. >>> + */ >>> +int ocfs2_inode_lock_tracker(struct inode *inode, >>> + struct buffer_head **ret_bh, >>> + int ex, >>> + struct ocfs2_lock_holder *oh) >>> +{ >>> + int status; >>> + int arg_flags = 0, has_locked; >>> + struct ocfs2_lock_res *lockres; >>> + >>> + lockres = &OCFS2_I(inode)->ip_inode_lockres; >>> + has_locked = ocfs2_is_locked_by_me(lockres); >>> + /* Just get buffer head if the cluster lock has been taken */ >>> + if (has_locked) >>> + arg_flags = OCFS2_META_LOCK_GETBH; >>> + >>> + if (likely(!has_locked || ret_bh)) { >>> + status = ocfs2_inode_lock_full(inode, ret_bh, ex, arg_flags); >>> + if (status < 0) { >>> + if (status != -ENOENT) >>> + mlog_errno(status); >>> + return status; >>> + } >>> + } >>> + if (!has_locked) >>> + ocfs2_add_holder(lockres, oh); >>> + >>> + return has_locked; >>> +} >>> + >>> +void ocfs2_inode_unlock_tracker(struct inode *inode, >>> + int ex, >>> + struct ocfs2_lock_holder *oh, >>> + int had_lock) >>> +{ >>> + struct ocfs2_lock_res *lockres; >>> + >>> + lockres = &OCFS2_I(inode)->ip_inode_lockres; >>> + if (!had_lock) { >>> + ocfs2_remove_holder(lockres, oh); >>> + ocfs2_inode_unlock(inode, ex); >>> + } >>> +} >>> + >>> int ocfs2_orphan_scan_lock(struct ocfs2_super *osb, u32 *seqno) >>> { >>> struct ocfs2_lock_res *lockres; >>> diff --git a/fs/ocfs2/dlmglue.h b/fs/ocfs2/dlmglue.h >>> index d293a22..a7fc18b 100644 >>> --- a/fs/ocfs2/dlmglue.h >>> +++ b/fs/ocfs2/dlmglue.h >>> @@ -70,6 +70,11 @@ struct ocfs2_orphan_scan_lvb { >>> __be32 lvb_os_seqno; >>> }; >>> +struct ocfs2_lock_holder { >>> + struct list_head oh_list; >>> + struct pid *oh_owner_pid; >>> +}; >>> + >>> /* ocfs2_inode_lock_full() 'arg_flags' flags */ >>> /* don't wait on recovery. */ >>> #define OCFS2_META_LOCK_RECOVERY (0x01) >>> @@ -77,6 +82,8 @@ struct ocfs2_orphan_scan_lvb { >>> #define OCFS2_META_LOCK_NOQUEUE (0x02) >>> /* don't block waiting for the downconvert thread, instead return >>> -EAGAIN */ >>> #define OCFS2_LOCK_NONBLOCK (0x04) >>> +/* just get back disk inode bh if we've got cluster lock. */ >>> +#define OCFS2_META_LOCK_GETBH (0x08) >>> /* Locking subclasses of inode cluster lock */ >>> enum { >>> @@ -170,4 +177,15 @@ void ocfs2_put_dlm_debug(struct ocfs2_dlm_debug >>> *dlm_debug); >>> /* To set the locking protocol on module initialization */ >>> void ocfs2_set_locking_protocol(void); >>> + >>> +/* The _tracker pair is used to avoid cluster recursive locking */ >>> +int ocfs2_inode_lock_tracker(struct inode *inode, >>> + struct buffer_head **ret_bh, >>> + int ex, >>> + struct ocfs2_lock_holder *oh); >>> +void ocfs2_inode_unlock_tracker(struct inode *inode, >>> + int ex, >>> + struct ocfs2_lock_holder *oh, >>> + int had_lock); >>> + >>> #endif /* DLMGLUE_H */ >>> diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h >>> index 7e5958b..0c39d71 100644 >>> --- a/fs/ocfs2/ocfs2.h >>> +++ b/fs/ocfs2/ocfs2.h >>> @@ -172,6 +172,7 @@ struct ocfs2_lock_res { >>> struct list_head l_blocked_list; >>> struct list_head l_mask_waiters; >>> + struct list_head l_holders; >>> unsigned long l_flags; >>> char l_name[OCFS2_LOCK_ID_MAX_LEN]; >> >> >