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Message-ID: <66ba9e8a-cdb7-fc79-2ea2-8c20efaf7604@suse.com>
Date: Mon, 16 Jan 2017 15:35:12 +0800
From: Eric Ren <zren@...e.com>
To: Junxiao Bi <junxiao.bi@...cle.com>, ocfs2-devel@....oracle.com
Cc: akpm@...ux-foundation.org, mfasheh@...sity.com, jlbec@...lplan.org,
ghe@...e.com, jiangqi903@...il.com, sfr@...b.auug.org.au,
hch@....de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] ocfs2: fix deadlock issue when taking inode lock
at vfs entry points
Hi!
On 01/16/2017 02:58 PM, Junxiao Bi wrote:
> On 01/16/2017 02:42 PM, Eric Ren wrote:
>> Commit 743b5f1434f5 ("ocfs2: take inode lock in ocfs2_iop_set/get_acl()")
>> results in a deadlock, as the author "Tariq Saeed" realized shortly
>> after the patch was merged. The discussion happened here
>> (https://oss.oracle.com/pipermail/ocfs2-devel/2015-September/011085.html).
>>
>> The reason why taking cluster inode lock at vfs entry points opens up
>> a self deadlock window, is explained in the previous patch of this
>> series.
>>
>> So far, we have seen two different code paths that have this issue.
>> 1. do_sys_open
>> may_open
>> inode_permission
>> ocfs2_permission
>> ocfs2_inode_lock() <=== take PR
>> generic_permission
>> get_acl
>> ocfs2_iop_get_acl
>> ocfs2_inode_lock() <=== take PR
>> 2. fchmod|fchmodat
>> chmod_common
>> notify_change
>> ocfs2_setattr <=== take EX
>> posix_acl_chmod
>> get_acl
>> ocfs2_iop_get_acl <=== take PR
>> ocfs2_iop_set_acl <=== take EX
>>
>> Fixes them by adding the tracking logic (in the previous patch) for
>> these funcs above, ocfs2_permission(), ocfs2_iop_[set|get]_acl(),
>> ocfs2_setattr().
>>
>> Changes since v1:
>> 1. Let ocfs2_is_locked_by_me() just return true/false to indicate if the
>> process gets the cluster lock - suggested by: Joseph Qi <jiangqi903@...il.com>
>> and Junxiao Bi <junxiao.bi@...cle.com>.
>>
>> 2. Change "struct ocfs2_holder" to a more meaningful name "ocfs2_lock_holder",
>> suggested by: Junxiao Bi <junxiao.bi@...cle.com>.
>>
>> 3. Add debugging output at ocfs2_setattr() and ocfs2_permission() to
>> catch exceptional cases, suggested by: Junxiao Bi <junxiao.bi@...cle.com>.
>>
>> Signed-off-by: Eric Ren <zren@...e.com>
>> ---
>> fs/ocfs2/acl.c | 39 +++++++++++++++++++++++++----
>> fs/ocfs2/file.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++--------
>> 2 files changed, 100 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
>> index bed1fcb..3e47262 100644
>> --- a/fs/ocfs2/acl.c
>> +++ b/fs/ocfs2/acl.c
>> @@ -284,16 +284,31 @@ int ocfs2_iop_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>> {
>> struct buffer_head *bh = NULL;
>> int status = 0;
>> -
>> - status = ocfs2_inode_lock(inode, &bh, 1);
>> + int arg_flags = 0, has_locked;
>> + struct ocfs2_lock_holder oh;
>> + struct ocfs2_lock_res *lockres;
>> +
>> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
>> + has_locked = ocfs2_is_locked_by_me(lockres);
>> + if (has_locked)
>> + arg_flags = OCFS2_META_LOCK_GETBH;
>> + status = ocfs2_inode_lock_full(inode, &bh, 1, arg_flags);
>> if (status < 0) {
>> if (status != -ENOENT)
>> mlog_errno(status);
>> return status;
>> }
>> + if (!has_locked)
>> + ocfs2_add_holder(lockres, &oh);
>> +
> Same code pattern showed here and *get_acl, can it be abstracted to one
> function?
> The same issue for *setattr and *permission. Sorry for not mention that
> in last review.
Good idea! I will do it in the next version;-)
Thanks,
Eric
>
> Thanks,
> Junxiao.
>> status = ocfs2_set_acl(NULL, inode, bh, type, acl, NULL, NULL);
>> - ocfs2_inode_unlock(inode, 1);
>> +
>> + if (!has_locked) {
>> + ocfs2_remove_holder(lockres, &oh);
>> + ocfs2_inode_unlock(inode, 1);
>> + }
>> brelse(bh);
>> +
>> return status;
>> }
>>
>> @@ -303,21 +318,35 @@ struct posix_acl *ocfs2_iop_get_acl(struct inode *inode, int type)
>> struct buffer_head *di_bh = NULL;
>> struct posix_acl *acl;
>> int ret;
>> + int arg_flags = 0, has_locked;
>> + struct ocfs2_lock_holder oh;
>> + struct ocfs2_lock_res *lockres;
>>
>> osb = OCFS2_SB(inode->i_sb);
>> if (!(osb->s_mount_opt & OCFS2_MOUNT_POSIX_ACL))
>> return NULL;
>> - ret = ocfs2_inode_lock(inode, &di_bh, 0);
>> +
>> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
>> + has_locked = ocfs2_is_locked_by_me(lockres);
>> + if (has_locked)
>> + arg_flags = OCFS2_META_LOCK_GETBH;
>> + ret = ocfs2_inode_lock_full(inode, &di_bh, 0, arg_flags);
>> if (ret < 0) {
>> if (ret != -ENOENT)
>> mlog_errno(ret);
>> return ERR_PTR(ret);
>> }
>> + if (!has_locked)
>> + ocfs2_add_holder(lockres, &oh);
>>
>> acl = ocfs2_get_acl_nolock(inode, type, di_bh);
>>
>> - ocfs2_inode_unlock(inode, 0);
>> + if (!has_locked) {
>> + ocfs2_remove_holder(lockres, &oh);
>> + ocfs2_inode_unlock(inode, 0);
>> + }
>> brelse(di_bh);
>> +
>> return acl;
>> }
>>
>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
>> index c488965..b620c25 100644
>> --- a/fs/ocfs2/file.c
>> +++ b/fs/ocfs2/file.c
>> @@ -1138,6 +1138,9 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>> handle_t *handle = NULL;
>> struct dquot *transfer_to[MAXQUOTAS] = { };
>> int qtype;
>> + int arg_flags = 0, had_lock;
>> + struct ocfs2_lock_holder oh;
>> + struct ocfs2_lock_res *lockres;
>>
>> trace_ocfs2_setattr(inode, dentry,
>> (unsigned long long)OCFS2_I(inode)->ip_blkno,
>> @@ -1173,13 +1176,41 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>> }
>> }
>>
>> - status = ocfs2_inode_lock(inode, &bh, 1);
>> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
>> + had_lock = ocfs2_is_locked_by_me(lockres);
>> + if (had_lock) {
>> + arg_flags = OCFS2_META_LOCK_GETBH;
>> +
>> + /*
>> + * As far as we know, ocfs2_setattr() could only be the first
>> + * VFS entry point in the call chain of recursive cluster
>> + * locking issue.
>> + *
>> + * For instance:
>> + * chmod_common()
>> + * notify_change()
>> + * ocfs2_setattr()
>> + * posix_acl_chmod()
>> + * ocfs2_iop_get_acl()
>> + *
>> + * But, we're not 100% sure if it's always true, because the
>> + * ordering of the VFS entry points in the call chain is out
>> + * of our control. So, we'd better dump the stack here to
>> + * catch the other cases of recursive locking.
>> + */
>> + mlog(ML_ERROR, "Another case of recursive locking:\n");
>> + dump_stack();
>> + }
>> + status = ocfs2_inode_lock_full(inode, &bh, 1, arg_flags);
>> if (status < 0) {
>> if (status != -ENOENT)
>> mlog_errno(status);
>> goto bail_unlock_rw;
>> }
>> - inode_locked = 1;
>> + if (!had_lock) {
>> + ocfs2_add_holder(lockres, &oh);
>> + inode_locked = 1;
>> + }
>>
>> if (size_change) {
>> status = inode_newsize_ok(inode, attr->ia_size);
>> @@ -1260,7 +1291,8 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>> bail_commit:
>> ocfs2_commit_trans(osb, handle);
>> bail_unlock:
>> - if (status) {
>> + if (status && inode_locked) {
>> + ocfs2_remove_holder(lockres, &oh);
>> ocfs2_inode_unlock(inode, 1);
>> inode_locked = 0;
>> }
>> @@ -1278,8 +1310,10 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>> if (status < 0)
>> mlog_errno(status);
>> }
>> - if (inode_locked)
>> + if (inode_locked) {
>> + ocfs2_remove_holder(lockres, &oh);
>> ocfs2_inode_unlock(inode, 1);
>> + }
>>
>> brelse(bh);
>> return status;
>> @@ -1321,20 +1355,42 @@ int ocfs2_getattr(struct vfsmount *mnt,
>> int ocfs2_permission(struct inode *inode, int mask)
>> {
>> int ret;
>> + int has_locked;
>> + struct ocfs2_lock_holder oh;
>> + struct ocfs2_lock_res *lockres;
>>
>> if (mask & MAY_NOT_BLOCK)
>> return -ECHILD;
>>
>> - ret = ocfs2_inode_lock(inode, NULL, 0);
>> - if (ret) {
>> - if (ret != -ENOENT)
>> - mlog_errno(ret);
>> - goto out;
>> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
>> + has_locked = ocfs2_is_locked_by_me(lockres);
>> + if (!has_locked) {
>> + ret = ocfs2_inode_lock(inode, NULL, 0);
>> + if (ret) {
>> + if (ret != -ENOENT)
>> + mlog_errno(ret);
>> + goto out;
>> + }
>> + ocfs2_add_holder(lockres, &oh);
>> + } else {
>> + /* See comments in ocfs2_setattr() for details.
>> + * The call chain of this case could be:
>> + * do_sys_open()
>> + * may_open()
>> + * inode_permission()
>> + * ocfs2_permission()
>> + * ocfs2_iop_get_acl()
>> + */
>> + mlog(ML_ERROR, "Another case of recursive locking:\n");
>> + dump_stack();
>> }
>>
>> ret = generic_permission(inode, mask);
>>
>> - ocfs2_inode_unlock(inode, 0);
>> + if (!has_locked) {
>> + ocfs2_remove_holder(lockres, &oh);
>> + ocfs2_inode_unlock(inode, 0);
>> + }
>> out:
>> return ret;
>> }
>>
>
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