cifs: Wait for writebacks to complete before attempting write.

Problem reported in Red Hat bz 1040329 for strict writes where we cache
only when we hold oplock and write direct to the server when we don't.

When we receive an oplock break, we first change the oplock value for
the inode in cifsInodeInfo->oplock to indicate that we no longer hold
the oplock before we enqueue a task to flush changes to the backing
device. Once we have completed flushing the changes, we return the
oplock to the server.

There are 2 ways here where we can have data corruption
1) While we flush changes to the backing device as part of the oplock
break, we can have processes write to the file. These writes check for
the oplock, find none and attempt to write directly to the server.
These direct writes made while we are flushing from cache could be
overwritten by data being flushed from the cache causing data
corruption.
2) While a thread runs in cifs_strict_writev, the machine could receive
and process an oplock break after the thread has checked the oplock and
found that it allows us to cache and before we have made changes to the
cache. In that case, we end up with a dirty page in cache when we
shouldn't have any. This will be flushed later and will overwrite all
subsequent writes to the part of the file represented by this page.

Before making any writes to the server, we need to confirm that we are
not in the process of flushing data to the server and if we are, we
should wait until the process is complete before we attempt the write.
We should also wait for existing writes to complete before we process
an oplock break request which changes oplock values.

We add a version specific  downgrade_oplock() operation to allow for
differences in the oplock values set for the different smb versions.

Cc: stable@vger.kernel.org
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsfs.c

@@ -253,6 +253,11 @@ cifs_alloc_inode(struct super_block *sb)
 	cifs_set_oplock_level(cifs_inode, 0);
 	cifs_inode->delete_pending = false;
 	cifs_inode->invalid_mapping = false;
+	clear_bit(CIFS_INODE_PENDING_OPLOCK_BREAK, &cifs_inode->flags);
+	clear_bit(CIFS_INODE_PENDING_WRITERS, &cifs_inode->flags);
+	clear_bit(CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2, &cifs_inode->flags);
+	spin_lock_init(&cifs_inode->writers_lock);
+	cifs_inode->writers = 0;
 	cifs_inode->vfs_inode.i_blkbits = 14;  /* 2**14 = CIFS_MAX_MSGSIZE */
 	cifs_inode->server_eof = 0;
 	cifs_inode->uniqueid = 0;
@@ -732,19 +737,26 @@ static ssize_t cifs_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 				   unsigned long nr_segs, loff_t pos)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
+	struct cifsInodeInfo *cinode = CIFS_I(inode);
 	ssize_t written;
 	int rc;
 
+	written = cifs_get_writer(cinode);
+	if (written)
+		return written;
+
 	written = generic_file_aio_write(iocb, iov, nr_segs, pos);
 
 	if (CIFS_CACHE_WRITE(CIFS_I(inode)))
-		return written;
+		goto out;
 
 	rc = filemap_fdatawrite(inode->i_mapping);
 	if (rc)
 		cifs_dbg(FYI, "cifs_file_aio_write: %d rc on %p inode\n",
 			 rc, inode);
 
+out:
+	cifs_put_writer(cinode);
 	return written;
 }
 

fs/cifs/cifsglob.h

@@ -228,6 +228,8 @@ struct smb_version_operations {
 	/* verify the message */
 	int (*check_message)(char *, unsigned int);
 	bool (*is_oplock_break)(char *, struct TCP_Server_Info *);
+	void (*downgrade_oplock)(struct TCP_Server_Info *,
+					struct cifsInodeInfo *, bool);
 	/* process transaction2 response */
 	bool (*check_trans2)(struct mid_q_entry *, struct TCP_Server_Info *,
 			     char *, int);
@@ -1113,6 +1115,12 @@ struct cifsInodeInfo {
 	unsigned int epoch;		/* used to track lease state changes */
 	bool delete_pending;		/* DELETE_ON_CLOSE is set */
 	bool invalid_mapping;		/* pagecache is invalid */
+	unsigned long flags;
+#define CIFS_INODE_PENDING_OPLOCK_BREAK   (0) /* oplock break in progress */
+#define CIFS_INODE_PENDING_WRITERS	  (1) /* Writes in progress */
+#define CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2 (2) /* Downgrade oplock to L2 */
+	spinlock_t writers_lock;
+	unsigned int writers;		/* Number of writers on this inode */
 	unsigned long time;		/* jiffies of last update of inode */
 	u64  server_eof;		/* current file size on server -- protected by i_lock */
 	u64  uniqueid;			/* server inode number */

fs/cifs/cifsproto.h

@@ -127,6 +127,9 @@ extern u64 cifs_UnixTimeToNT(struct timespec);
 extern struct timespec cnvrtDosUnixTm(__le16 le_date, __le16 le_time,
 				      int offset);
 extern void cifs_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock);
+extern int cifs_get_writer(struct cifsInodeInfo *cinode);
+extern void cifs_put_writer(struct cifsInodeInfo *cinode);
+extern void cifs_done_oplock_break(struct cifsInodeInfo *cinode);
 extern int cifs_unlock_range(struct cifsFileInfo *cfile,
 			     struct file_lock *flock, const unsigned int xid);
 extern int cifs_push_mandatory_locks(struct cifsFileInfo *cfile);

fs/cifs/file.c

@@ -2621,12 +2621,20 @@ cifs_strict_writev(struct kiocb *iocb, const struct iovec *iov,
 	struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
 	ssize_t written;
 
+	written = cifs_get_writer(cinode);
+	if (written)
+		return written;
+
 	if (CIFS_CACHE_WRITE(cinode)) {
 		if (cap_unix(tcon->ses) &&
 		(CIFS_UNIX_FCNTL_CAP & le64_to_cpu(tcon->fsUnixInfo.Capability))
-		    && ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOPOSIXBRL) == 0))
-			return generic_file_aio_write(iocb, iov, nr_segs, pos);
-		return cifs_writev(iocb, iov, nr_segs, pos);
+		  && ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOPOSIXBRL) == 0)) {
+			written = generic_file_aio_write(
+					iocb, iov, nr_segs, pos);
+			goto out;
+		}
+		written = cifs_writev(iocb, iov, nr_segs, pos);
+		goto out;
 	}
 	/*
 	 * For non-oplocked files in strict cache mode we need to write the data
@@ -2646,6 +2654,8 @@ cifs_strict_writev(struct kiocb *iocb, const struct iovec *iov,
 			 inode);
 		cinode->oplock = 0;
 	}
+out:
+	cifs_put_writer(cinode);
 	return written;
 }
 
@@ -3621,6 +3631,13 @@ static int cifs_launder_page(struct page *page)
 	return rc;
 }
 
+static int
+cifs_pending_writers_wait(void *unused)
+{
+	schedule();
+	return 0;
+}
+
 void cifs_oplock_break(struct work_struct *work)
 {
 	struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
@@ -3628,8 +3645,15 @@ void cifs_oplock_break(struct work_struct *work)
 	struct inode *inode = cfile->dentry->d_inode;
 	struct cifsInodeInfo *cinode = CIFS_I(inode);
 	struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
+	struct TCP_Server_Info *server = tcon->ses->server;
 	int rc = 0;
 
+	wait_on_bit(&cinode->flags, CIFS_INODE_PENDING_WRITERS,
+			cifs_pending_writers_wait, TASK_UNINTERRUPTIBLE);
+
+	server->ops->downgrade_oplock(server, cinode,
+		test_bit(CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2, &cinode->flags));
+
 	if (!CIFS_CACHE_WRITE(cinode) && CIFS_CACHE_READ(cinode) &&
 						cifs_has_mand_locks(cinode)) {
 		cifs_dbg(FYI, "Reset oplock to None for inode=%p due to mand locks\n",
@@ -3666,6 +3690,7 @@ void cifs_oplock_break(struct work_struct *work)
 							     cinode);
 		cifs_dbg(FYI, "Oplock release rc = %d\n", rc);
 	}
+	cifs_done_oplock_break(cinode);
 }
 
 /*

fs/cifs/misc.c

@@ -466,8 +466,22 @@ is_valid_oplock_break(char *buffer, struct TCP_Server_Info *srv)
 				cifs_dbg(FYI, "file id match, oplock break\n");
 				pCifsInode = CIFS_I(netfile->dentry->d_inode);
 
-				cifs_set_oplock_level(pCifsInode,
-					pSMB->OplockLevel ? OPLOCK_READ : 0);
+				set_bit(CIFS_INODE_PENDING_OPLOCK_BREAK,
+					&pCifsInode->flags);
+
+				/*
+				 * Set flag if the server downgrades the oplock
+				 * to L2 else clear.
+				 */
+				if (pSMB->OplockLevel)
+					set_bit(
+					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
+					   &pCifsInode->flags);
+				else
+					clear_bit(
+					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
+					   &pCifsInode->flags);
+
 				queue_work(cifsiod_wq,
 					   &netfile->oplock_break);
 				netfile->oplock_break_cancelled = false;
@@ -551,6 +565,62 @@ void cifs_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock)
 		cinode->oplock = 0;
 }
 
+static int
+cifs_oplock_break_wait(void *unused)
+{
+	schedule();
+	return signal_pending(current) ? -ERESTARTSYS : 0;
+}
+
+/*
+ * We wait for oplock breaks to be processed before we attempt to perform
+ * writes.
+ */
+int cifs_get_writer(struct cifsInodeInfo *cinode)
+{
+	int rc;
+
+start:
+	rc = wait_on_bit(&cinode->flags, CIFS_INODE_PENDING_OPLOCK_BREAK,
+				   cifs_oplock_break_wait, TASK_KILLABLE);
+	if (rc)
+		return rc;
+
+	spin_lock(&cinode->writers_lock);
+	if (!cinode->writers)
+		set_bit(CIFS_INODE_PENDING_WRITERS, &cinode->flags);
+	cinode->writers++;
+	/* Check to see if we have started servicing an oplock break */
+	if (test_bit(CIFS_INODE_PENDING_OPLOCK_BREAK, &cinode->flags)) {
+		cinode->writers--;
+		if (cinode->writers == 0) {
+			clear_bit(CIFS_INODE_PENDING_WRITERS, &cinode->flags);
+			wake_up_bit(&cinode->flags, CIFS_INODE_PENDING_WRITERS);
+		}
+		spin_unlock(&cinode->writers_lock);
+		goto start;
+	}
+	spin_unlock(&cinode->writers_lock);
+	return 0;
+}
+
+void cifs_put_writer(struct cifsInodeInfo *cinode)
+{
+	spin_lock(&cinode->writers_lock);
+	cinode->writers--;
+	if (cinode->writers == 0) {
+		clear_bit(CIFS_INODE_PENDING_WRITERS, &cinode->flags);
+		wake_up_bit(&cinode->flags, CIFS_INODE_PENDING_WRITERS);
+	}
+	spin_unlock(&cinode->writers_lock);
+}
+
+void cifs_done_oplock_break(struct cifsInodeInfo *cinode)
+{
+	clear_bit(CIFS_INODE_PENDING_OPLOCK_BREAK, &cinode->flags);
+	wake_up_bit(&cinode->flags, CIFS_INODE_PENDING_OPLOCK_BREAK);
+}
+
 bool
 backup_cred(struct cifs_sb_info *cifs_sb)
 {

fs/cifs/smb1ops.c

@@ -372,6 +372,16 @@ coalesce_t2(char *second_buf, struct smb_hdr *target_hdr)
 	return 0;
 }
 
+static void
+cifs_downgrade_oplock(struct TCP_Server_Info *server,
+			struct cifsInodeInfo *cinode, bool set_level2)
+{
+	if (set_level2)
+		cifs_set_oplock_level(cinode, OPLOCK_READ);
+	else
+		cifs_set_oplock_level(cinode, 0);
+}
+
 static bool
 cifs_check_trans2(struct mid_q_entry *mid, struct TCP_Server_Info *server,
 		  char *buf, int malformed)
@@ -1019,6 +1029,7 @@ struct smb_version_operations smb1_operations = {
 	.clear_stats = cifs_clear_stats,
 	.print_stats = cifs_print_stats,
 	.is_oplock_break = is_valid_oplock_break,
+	.downgrade_oplock = cifs_downgrade_oplock,
 	.check_trans2 = cifs_check_trans2,
 	.need_neg = cifs_need_neg,
 	.negotiate = cifs_negotiate,

fs/cifs/smb2misc.c

@@ -575,9 +575,21 @@ smb2_is_valid_oplock_break(char *buffer, struct TCP_Server_Info *server)
 				else
 					cfile->oplock_break_cancelled = false;
 
-				server->ops->set_oplock_level(cinode,
-				  rsp->OplockLevel ? SMB2_OPLOCK_LEVEL_II : 0,
-				  0, NULL);
+				set_bit(CIFS_INODE_PENDING_OPLOCK_BREAK,
+					&cinode->flags);
+
+				/*
+				 * Set flag if the server downgrades the oplock
+				 * to L2 else clear.
+				 */
+				if (rsp->OplockLevel)
+					set_bit(
+					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
+					   &cinode->flags);
+				else
+					clear_bit(
+					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
+					   &cinode->flags);
 
 				queue_work(cifsiod_wq, &cfile->oplock_break);
 

fs/cifs/smb2ops.c

@@ -904,6 +904,17 @@ smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
 	return rc;
 }
 
+static void
+smb2_downgrade_oplock(struct TCP_Server_Info *server,
+			struct cifsInodeInfo *cinode, bool set_level2)
+{
+	if (set_level2)
+		server->ops->set_oplock_level(cinode, SMB2_OPLOCK_LEVEL_II,
+						0, NULL);
+	else
+		server->ops->set_oplock_level(cinode, 0, 0, NULL);
+}
+
 static void
 smb2_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock,
 		      unsigned int epoch, bool *purge_cache)
@@ -1110,6 +1121,7 @@ struct smb_version_operations smb20_operations = {
 	.clear_stats = smb2_clear_stats,
 	.print_stats = smb2_print_stats,
 	.is_oplock_break = smb2_is_valid_oplock_break,
+	.downgrade_oplock = smb2_downgrade_oplock,
 	.need_neg = smb2_need_neg,
 	.negotiate = smb2_negotiate,
 	.negotiate_wsize = smb2_negotiate_wsize,
@@ -1184,6 +1196,7 @@ struct smb_version_operations smb21_operations = {
 	.clear_stats = smb2_clear_stats,
 	.print_stats = smb2_print_stats,
 	.is_oplock_break = smb2_is_valid_oplock_break,
+	.downgrade_oplock = smb2_downgrade_oplock,
 	.need_neg = smb2_need_neg,
 	.negotiate = smb2_negotiate,
 	.negotiate_wsize = smb2_negotiate_wsize,
@@ -1259,6 +1272,7 @@ struct smb_version_operations smb30_operations = {
 	.print_stats = smb2_print_stats,
 	.dump_share_caps = smb2_dump_share_caps,
 	.is_oplock_break = smb2_is_valid_oplock_break,
+	.downgrade_oplock = smb2_downgrade_oplock,
 	.need_neg = smb2_need_neg,
 	.negotiate = smb2_negotiate,
 	.negotiate_wsize = smb2_negotiate_wsize,