Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points

[Joseph Qi]

On 17/1/6 14:56, Eric Ren wrote:
On 01/06/2017 02:09 PM, Joseph Qi wrote:
Hi Eric,


On 17/1/5 23:31, 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().
As described cases above, shall we just add the tracking logic only 
for set/get_acl()?

The idea is to detect recursive locking on the running task stack. 
Take case 1) for example if ocfs2_permisssion()
is not changed:

ocfs2_permission() <=== take PR, ocfs2_holder is not added
   ocfs2_iop_get_acl <=== still take PR, because there is no lock 
holder on the tracking list
I mean we have no need to check if locked by me, just do inode lock and 
add holder.
This will make code more clean, IMO.

Thanks,
Joseph

Thanks for your review;-)
Eric


Thanks,
Joseph

Signed-off-by: Eric Ren <z...@suse.com>
---
  fs/ocfs2/acl.c  | 39 ++++++++++++++++++++++++++++++++++-----
  fs/ocfs2/file.c | 44 ++++++++++++++++++++++++++++++++++----------
  2 files changed, 68 insertions(+), 15 deletions(-)

diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
index bed1fcb..c539890 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_holder oh;
+    struct ocfs2_lock_res *lockres;
+
+    lockres = &OCFS2_I(inode)->ip_inode_lockres;
+    has_locked = (ocfs2_is_locked_by_me(lockres) != NULL);
+    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_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) != NULL);
+    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..62be75d 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_holder oh;
+    struct ocfs2_lock_res *lockres;
        trace_ocfs2_setattr(inode, dentry,
                  (unsigned long long)OCFS2_I(inode)->ip_blkno,
@@ -1173,13 +1176,20 @@ 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) != NULL);
+    if (had_lock)
+        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);
          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 +1270,8 @@ 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 +1289,10 @@ 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 +1334,31 @@ int ocfs2_getattr(struct vfsmount *mnt,
  int ocfs2_permission(struct inode *inode, int mask)
  {
      int ret;
+    int has_locked;
+    struct ocfs2_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) != NULL);
+    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);
      }
        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;
  }