Changeset f0fdc7d in mainline

Timestamp:

2011-03-21T00:11:31Z (13 years ago)

Author:

Vojtech Horky <vojtechhorky@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

2e1d5d70, 79c8a96

Parents:

00c18bc

Message:

Fix race condition in driver - HC communication

See diff for explanation of the race.

This commit fixes problem described in ticket 143
(​https://sourceforge.net/apps/trac/helenos-usb/ticket/143).

File:

• uspace/lib/usb/src/pipes.c (modified) (2 diffs)

uspace/lib/usb/src/pipes.c

@@ -42 +42 @@
 #include <assert.h>
 
+#define IPC_AGAIN_DELAY (1000 * 2) /* 2ms */
+
 /** Tell USB address assigned to given device.
  *
@@ -150 +152 @@
         }
 
-        my_address = get_my_address(parent_phone, dev);
-        if (my_address < 0) {
-                rc = my_address;
-                goto leave;
-        }
+        /*
+         * Asking for "my" address may require several attempts.
+         * That is because following scenario may happen:
+         *  - parent driver (i.e. driver of parent device) announces new device
+         *    and devman launches current driver
+         *  - parent driver is preempted and thus does not send address-handle
+         *    binding to HC driver
+         *  - this driver gets here and wants the binding
+         *  - the HC does not know the binding yet and thus it answers ENOENT
+         *  So, we need to wait for the HC to learn the binding.
+         */
+        do {
+                my_address = get_my_address(parent_phone, dev);
+
+                if (my_address == ENOENT) {
+                        /* Be nice, let other fibrils run and try again. */
+                        async_usleep(IPC_AGAIN_DELAY);
+                } else if (my_address < 0) {
+                        /* Some other problem, no sense trying again. */
+                        rc = my_address;
+                        goto leave;
+                }
+
+        } while (my_address < 0);
 
         rc = usb_device_connection_initialize(connection,