cifs: convert oplock breaks to use slow_work facility (try #4)

This is the fourth respin of the patch to convert oplock breaks to
use the slow_work facility.

A customer of ours was testing a backport of one of the earlier
patchsets, and hit a "Busy inodes after umount..." problem. An oplock
break job had raced with a umount, and the superblock got torn down and
its memory reused. When the oplock break job tried to dereference the
inode->i_sb, the kernel oopsed.

This patchset has the oplock break job hold an inode and vfsmount
reference until the oplock break completes.  With this, there should be
no need to take a tcon reference (the vfsmount implicitly holds one
already).

Currently, when an oplock break comes in there's a chance that the
oplock break job won't occur if the allocation of the oplock_q_entry
fails. There are also some rather nasty races in the allocation and
handling these structs.

Rather than allocating oplock queue entries when an oplock break comes
in, add a few extra fields to the cifsFileInfo struct. Get rid of the
dedicated cifs_oplock_thread as well and queue the oplock break job to
the slow_work thread pool.

This approach also has the advantage that the oplock break jobs can
potentially run in parallel rather than be serialized like they are
today.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 20 insertions, 9 deletions

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index 191e622..0241b25 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -32,7 +32,6 @@
 
 extern mempool_t *cifs_sm_req_poolp;
 extern mempool_t *cifs_req_poolp;
-extern struct task_struct *oplockThread;
 
 /* The xid serves as a useful identifier for each incoming vfs request,
    in a similar way to the mid which is useful to track each sent smb,
@@ -500,6 +499,7 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
 	struct cifsTconInfo *tcon;
 	struct cifsInodeInfo *pCifsInode;
 	struct cifsFileInfo *netfile;
+	int rc;
 
 	cFYI(1, ("Checking for oplock break or dnotify response"));
 	if ((pSMB->hdr.Command == SMB_COM_NT_TRANSACT) &&
@@ -569,19 +569,30 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
 				if (pSMB->Fid != netfile->netfid)
 					continue;
 
-				read_unlock(&GlobalSMBSeslock);
-				read_unlock(&cifs_tcp_ses_lock);
+				/*
+				 * don't do anything if file is about to be
+				 * closed anyway.
+				 */
+				if (netfile->closePend) {
+					read_unlock(&GlobalSMBSeslock);
+					read_unlock(&cifs_tcp_ses_lock);
+					return true;
+				}
+
 				cFYI(1, ("file id match, oplock break"));
 				pCifsInode = CIFS_I(netfile->pInode);
 				pCifsInode->clientCanCacheAll = false;
 				if (pSMB->OplockLevel == 0)
 					pCifsInode->clientCanCacheRead = false;
-				AllocOplockQEntry(netfile->pInode,
-						  netfile->netfid, tcon);
-				cFYI(1, ("about to wake up oplock thread"));
-				if (oplockThread)
-					wake_up_process(oplockThread);
-
+				rc = slow_work_enqueue(&netfile->oplock_break);
+				if (rc) {
+					cERROR(1, ("failed to enqueue oplock "
+						   "break: %d\n", rc));
+				} else {
+					netfile->oplock_break_cancelled = false;
+				}
+				read_unlock(&GlobalSMBSeslock);
+				read_unlock(&cifs_tcp_ses_lock);
 				return true;
 			}
 			read_unlock(&GlobalSMBSeslock);