[Ocfs2-devel] [PATCH v2 2/2] ocfs2: fix deadlock issue when taking inode lock at vfs entry points
Eric Ren
zren at suse.com
Sun Jan 15 22:42:20 PST 2017
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 at gmail.com>
and Junxiao Bi <junxiao.bi at oracle.com>.
2. Change "struct ocfs2_holder" to a more meaningful name "ocfs2_lock_holder",
suggested by: Junxiao Bi <junxiao.bi at oracle.com>.
3. Add debugging output at ocfs2_setattr() and ocfs2_permission() to
catch exceptional cases, suggested by: Junxiao Bi <junxiao.bi at oracle.com>.
Signed-off-by: Eric Ren <zren at suse.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);
+
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;
}
--
2.10.2
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