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, 5 insertions, 7 deletions

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index c19419a38f62..5d0fde18039c 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -18,6 +18,7 @@
  */
 #include <linux/in.h>
 #include <linux/in6.h>
+#include <linux/slow-work.h>
 #include "cifs_fs_sb.h"
 #include "cifsacl.h"
 /*
@@ -346,14 +347,16 @@ struct cifsFileInfo {
         /* lock scope id (0 if none) */
         struct file *pfile; /* needed for writepage */
         struct inode *pInode; /* needed for oplock break */
+        struct vfsmount *mnt;
         struct mutex lock_mutex;
         struct list_head llist; /* list of byte range locks we have. */
         bool closePend:1;       /* file is marked to close */
         bool invalidHandle:1;   /* file closed via session abend */
-        bool messageMode:1;     /* for pipes: message vs byte mode */
+        bool oplock_break_cancelled:1;
         atomic_t count;         /* reference count */
         struct mutex fh_mutex; /* prevents reopen race after dead ses*/
         struct cifs_search_info srch_inf;
+        struct slow_work oplock_break; /* slow_work job for oplock breaks */
 };
 
 /* Take a reference on the file private data */
@@ -670,12 +673,6 @@ GLOBAL_EXTERN rwlock_t		cifs_tcp_ses_lock;
  */
 GLOBAL_EXTERN rwlock_t GlobalSMBSeslock;
 
-/* Global list of oplocks */
-GLOBAL_EXTERN struct list_head cifs_oplock_list;
-
-/* Protects the cifs_oplock_list */
-GLOBAL_EXTERN spinlock_t cifs_oplock_lock;
-
 /* Outstanding dir notify requests */
 GLOBAL_EXTERN struct list_head GlobalDnotifyReqList;
 /* DirNotify response queue */
@@ -726,3 +723,4 @@ GLOBAL_EXTERN unsigned int cifs_min_rcv;    /* min size of big ntwrk buf pool */
 GLOBAL_EXTERN unsigned int cifs_min_small;  /* min size of small buf pool */
 GLOBAL_EXTERN unsigned int cifs_max_pending; /* MAX requests at once to server*/
 
+extern const struct slow_work_ops cifs_oplock_break_ops;