Still on the subject of UML hanging after VFS: mount, related to my earlier email (*), I've been trying to dig deeper into what causes the hang. When UML hangs, I observe the main thread idling, and 3 threads being blocked in either io_getevents, read, or poll. The thread stuck in read, in particular, is the device driver thread for the ubd driver, which waits on a socketpair type for requests. Initially, I suspected a bug or race condition in the code that manages the synchronization between these threads, resulting in a lost wakeup - specifically, a SIGIO that may not be delivered or ignored, preventing the corresponding ubd_interrupt() from not being called. However, I'm now beginning to have doubt whether this is in fact the reason. I added printk's to verify that all sent requests are received and processed.
Upon closer examination, I observed a fifth thread that is stopped while being ptraced (status reported as "T+" in ps.) I am surmising that this fifth may be the init process or another thread that performs some delayed initialization tasks. Unfortunately, since it's being ptraced, I cannot attach gdb to it. Does anybody knowledgeable with UML happen to know which thread that is so I could figure out where this thread is stuck? I assume that it may be related to UML's ptrace-based system call emulation, but I have not yet looked deeper into the implementation details. On a possibly related note, I would also like to know about where the belief that the hang issue is related to "confusion about VDSO" is coming from. - Godmar (*) http://sourceforge.net/mailarchive/message.php?msg_name=719dced30709050613y73887e87x22e032332c9bb38d%40mail.gmail.com ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ User-mode-linux-user mailing list User-mode-linux-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-user
