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, 72 insertions, 2 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index b976cea24102..90f61786f516 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -30,6 +30,7 @@
 #include <linux/writeback.h>
 #include <linux/task_io_accounting_ops.h>
 #include <linux/delay.h>
+#include <linux/mount.h>
 #include <asm/div64.h>
 #include "cifsfs.h"
 #include "cifspdu.h"
@@ -51,11 +52,13 @@ static inline struct cifsFileInfo *cifs_init_private(
         INIT_LIST_HEAD(&private_data->llist);
         private_data->pfile = file; /* needed for writepage */
         private_data->pInode = igrab(inode);
+        private_data->mnt = file->f_path.mnt;
         private_data->invalidHandle = false;
         private_data->closePend = false;
         /* Initialize reference count to one.  The private data is
         freed on the release of the last reference */
         atomic_set(&private_data->count, 1);
+        slow_work_init(&private_data->oplock_break, &cifs_oplock_break_ops);
 
         return private_data;
 }
@@ -327,7 +330,7 @@ int cifs_open(struct inode *inode, struct file *file)
                         le64_to_cpu(tcon->fsUnixInfo.Capability))) {
                 int oflags = (int) cifs_posix_convert_flags(file->f_flags);
                 /* can not refresh inode info since size could be stale */
-                rc = cifs_posix_open(full_path, &inode, inode->i_sb,
+                rc = cifs_posix_open(full_path, &inode, file->f_path.mnt,
                                      cifs_sb->mnt_file_mode /* ignored */,
                                      oflags, &oplock, &netfid, xid);
                 if (rc == 0) {
@@ -547,7 +550,7 @@ reopen_error_exit:
                         le64_to_cpu(tcon->fsUnixInfo.Capability))) {
                 int oflags = (int) cifs_posix_convert_flags(file->f_flags);
                 /* can not refresh inode info since size could be stale */
-                rc = cifs_posix_open(full_path, NULL, inode->i_sb,
+                rc = cifs_posix_open(full_path, NULL, file->f_path.mnt,
                                      cifs_sb->mnt_file_mode /* ignored */,
                                      oflags, &oplock, &netfid, xid);
                 if (rc == 0) {
@@ -2312,6 +2315,73 @@ out:
         return rc;
 }
 
+static void
+cifs_oplock_break(struct slow_work *work)
+{
+        struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
+                                                  oplock_break);
+        struct inode *inode = cfile->pInode;
+        struct cifsInodeInfo *cinode = CIFS_I(inode);
+        struct cifs_sb_info *cifs_sb = CIFS_SB(cfile->mnt->mnt_sb);
+        int rc, waitrc = 0;
+
+        if (inode && S_ISREG(inode->i_mode)) {
+#ifdef CONFIG_CIFS_EXPERIMENTAL
+                if (cinode->clientCanCacheAll == 0)
+                        break_lease(inode, FMODE_READ);
+                else if (cinode->clientCanCacheRead == 0)
+                        break_lease(inode, FMODE_WRITE);
+#endif
+                rc = filemap_fdatawrite(inode->i_mapping);
+                if (cinode->clientCanCacheRead == 0) {
+                        waitrc = filemap_fdatawait(inode->i_mapping);
+                        invalidate_remote_inode(inode);
+                }
+                if (!rc)
+                        rc = waitrc;
+                if (rc)
+                        cinode->write_behind_rc = rc;
+                cFYI(1, ("Oplock flush inode %p rc %d", inode, rc));
+        }
+
+        /*
+         * releasing stale oplock after recent reconnect of smb session using
+         * a now incorrect file handle is not a data integrity issue but do
+         * not bother sending an oplock release if session to server still is
+         * disconnected since oplock already released by the server
+         */
+        if (!cfile->closePend && !cfile->oplock_break_cancelled) {
+                rc = CIFSSMBLock(0, cifs_sb->tcon, cfile->netfid, 0, 0, 0, 0,
+                                 LOCKING_ANDX_OPLOCK_RELEASE, false);
+                cFYI(1, ("Oplock release rc = %d", rc));
+        }
+}
+
+static int
+cifs_oplock_break_get(struct slow_work *work)
+{
+        struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
+                                                  oplock_break);
+        mntget(cfile->mnt);
+        cifsFileInfo_get(cfile);
+        return 0;
+}
+
+static void
+cifs_oplock_break_put(struct slow_work *work)
+{
+        struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
+                                                  oplock_break);
+        mntput(cfile->mnt);
+        cifsFileInfo_put(cfile);
+}
+
+const struct slow_work_ops cifs_oplock_break_ops = {
+        .get_ref        = cifs_oplock_break_get,
+        .put_ref        = cifs_oplock_break_put,
+        .execute        = cifs_oplock_break,
+};
+
 const struct address_space_operations cifs_addr_ops = {
         .readpage = cifs_readpage,
         .readpages = cifs_readpages,