scsi: cxlflash: Transition to application close model

Caching the adapter file descriptor and performing a close on behalf of
an application is a poor design. This is due to the fact that once a
file descriptor in installed, it is free to be altered without the
knowledge of the cxlflash driver. This can lead to inconsistencies
between the application and kernel. Furthermore, the nature of the
former design is more exploitable and thus should be abandoned.

To support applications performing a close on the adapter file that is
associated with a context, a new flag is introduced to the user API to
indicate to applications that they are responsible for the close
following the cleanup (detach) of a context. The documentation is also
updated to reflect this change in behavior.

Inspired-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Acked-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 19 insertions, 52 deletions

diff --git a/drivers/scsi/cxlflash/superpipe.c b/drivers/scsi/cxlflash/superpipe.c
index be7522ae02a4..b3bb90df4e1f 100644
--- a/drivers/scsi/cxlflash/superpipe.c
+++ b/drivers/scsi/cxlflash/superpipe.c
@@ -825,7 +825,6 @@ static void remove_context(struct kref *kref)
 {
 	struct ctx_info *ctxi = container_of(kref, struct ctx_info, kref);
 	struct cxlflash_cfg *cfg = ctxi->cfg;
-	int lfd;
 	u64 ctxid = DECODE_CTXID(ctxi->ctxid);
 
 	/* Remove context from table/error list */
@@ -842,19 +841,7 @@ static void remove_context(struct kref *kref)
 	mutex_unlock(&ctxi->mutex);
 
 	/* Context now completely uncoupled/unreachable */
-	lfd = ctxi->lfd;
 	destroy_context(cfg, ctxi);
-
-	/*
-	 * As a last step, clean up external resources when not
-	 * already on an external cleanup thread, i.e.: close(adap_fd).
-	 *
-	 * NOTE: this will free up the context from the CXL services,
-	 * allowing it to dole out the same context_id on a future
-	 * (or even currently in-flight) disk_attach operation.
-	 */
-	if (lfd != -1)
-		sys_close(lfd);
 }
 
 /**
@@ -949,34 +936,18 @@ static int cxlflash_disk_detach(struct scsi_device *sdev,
  *
  * This routine is the release handler for the fops registered with
  * the CXL services on an initial attach for a context. It is called
- * when a close is performed on the adapter file descriptor returned
- * to the user. Programmatically, the user is not required to perform
- * the close, as it is handled internally via the detach ioctl when
- * a context is being removed. Note that nothing prevents the user
- * from performing a close, but the user should be aware that doing
- * so is considered catastrophic and subsequent usage of the superpipe
- * API with previously saved off tokens will fail.
+ * when a close (explicity by the user or as part of a process tear
+ * down) is performed on the adapter file descriptor returned to the
+ * user. The user should be aware that explicitly performing a close
+ * considered catastrophic and subsequent usage of the superpipe API
+ * with previously saved off tokens will fail.
  *
- * When initiated from an external close (either by the user or via
- * a process tear down), the routine derives the context reference
- * and calls detach for each LUN associated with the context. The
- * final detach operation will cause the context itself to be freed.
- * Note that the saved off lfd is reset prior to calling detach to
- * signify that the final detach should not perform a close.
- *
- * When initiated from a detach operation as part of the tear down
- * of a context, the context is first completely freed and then the
- * close is performed. This routine will fail to derive the context
- * reference (due to the context having already been freed) and then
- * call into the CXL release entry point.
- *
- * Thus, with exception to when the CXL process element (context id)
- * lookup fails (a case that should theoretically never occur), every
- * call into this routine results in a complete freeing of a context.
- *
- * As part of the detach, all per-context resources associated with the LUN
- * are cleaned up. When detaching the last LUN for a context, the context
- * itself is cleaned up and released.
+ * This routine derives the context reference and calls detach for
+ * each LUN associated with the context.The final detach operation
+ * causes the context itself to be freed. With exception to when the
+ * CXL process element (context id) lookup fails (a case that should
+ * theoretically never occur), every call into this routine results
+ * in a complete freeing of a context.
  *
  * Return: 0 on success
  */
@@ -1014,11 +985,8 @@ static int cxlflash_cxl_release(struct inode *inode, struct file *file)
 		goto out;
 	}
 
-	dev_dbg(dev, "%s: close(%d) for context %d\n",
-		__func__, ctxi->lfd, ctxid);
+	dev_dbg(dev, "%s: close for context %d\n", __func__, ctxid);
 
-	/* Reset the file descriptor to indicate we're on a close() thread */
-	ctxi->lfd = -1;
 	detach.context_id = ctxi->ctxid;
 	list_for_each_entry_safe(lun_access, t, &ctxi->luns, list)
 		_cxlflash_disk_detach(lun_access->sdev, ctxi, &detach);
@@ -1391,7 +1359,6 @@ static int cxlflash_disk_attach(struct scsi_device *sdev,
 			__func__, rctxid);
 		kref_get(&ctxi->kref);
 		list_add(&lun_access->list, &ctxi->luns);
-		fd = ctxi->lfd;
 		goto out_attach;
 	}
 
@@ -1461,7 +1428,11 @@ static int cxlflash_disk_attach(struct scsi_device *sdev,
 	fd_install(fd, file);
 
 out_attach:
-	attach->hdr.return_flags = 0;
+	if (fd != -1)
+		attach->hdr.return_flags = DK_CXLFLASH_APP_CLOSE_ADAP_FD;
+	else
+		attach->hdr.return_flags = 0;
+
 	attach->context_id = ctxi->ctxid;
 	attach->block_size = gli->blk_len;
 	attach->mmio_size = sizeof(afu->afu_map->hosts[0].harea);
@@ -1526,7 +1497,7 @@ static int recover_context(struct cxlflash_cfg *cfg, struct ctx_info *ctxi)
 {
 	struct device *dev = &cfg->dev->dev;
 	int rc = 0;
-	int old_fd, fd = -1;
+	int fd = -1;
 	int ctxid = -1;
 	struct file *file;
 	struct cxl_context *ctx;
@@ -1574,7 +1545,6 @@ static int recover_context(struct cxlflash_cfg *cfg, struct ctx_info *ctxi)
 	 * No error paths after this point. Once the fd is installed it's
 	 * visible to user space and can't be undone safely on this thread.
 	 */
-	old_fd = ctxi->lfd;
 	ctxi->ctxid = ENCODE_CTXID(ctxi, ctxid);
 	ctxi->lfd = fd;
 	ctxi->ctx = ctx;
@@ -1593,9 +1563,6 @@ static int recover_context(struct cxlflash_cfg *cfg, struct ctx_info *ctxi)
 	cfg->ctx_tbl[ctxid] = ctxi;
 	mutex_unlock(&cfg->ctx_tbl_list_mutex);
 	fd_install(fd, file);
-
-	/* Release the original adapter fd and associated CXL resources */
-	sys_close(old_fd);
 out:
 	dev_dbg(dev, "%s: returning ctxid=%d fd=%d rc=%d\n",
 		__func__, ctxid, fd, rc);
@@ -1707,7 +1674,7 @@ retry_recover:
 		recover->context_id = ctxi->ctxid;
 		recover->adap_fd = ctxi->lfd;
 		recover->mmio_size = sizeof(afu->afu_map->hosts[0].harea);
-		recover->hdr.return_flags |=
+		recover->hdr.return_flags = DK_CXLFLASH_APP_CLOSE_ADAP_FD |
 			DK_CXLFLASH_RECOVER_AFU_CONTEXT_RESET;
 		goto out;
 	}