Date: Sun, 28 Jul 2002 21:51:57 +0900 From: Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> To: current@FreeBSD.org Cc: Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> Subject: A fix of recent bugs in swapping in/out a process Message-ID: <200207281252.g6SCpvSH064272@silver.carrots.uucp.r.dl.itc.u-tokyo.ac.jp>
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If you are having a trouble of a broken thread state (eg a thread with TDS_RUNQ on no run queue) or a mysterious page fault on a kernel memory (probably in mi_switch()), you may want to try my patch at: http://people.FreeBSD.org/~tanimura/patches/procswap.diff.gz In a nutshell, this patch fixes three bugs: 1. a thread with TDS_RUNQ on no run queue. This is due to wakeup() and wakeup_one() setting the state to a thread to TDS_RUNQ even if the thread has been swapped out. As a thread being or having been swapped out cannot be scheduled immediately, introduce a new thread state TDS_SWAPPED to note that. 2. a possible race condition for multiple threads to swap in a single process. Since faultin() may block (and likely to do so) without leaving any flags for a process being swapped in, more than one threads can call faultin() for the same process. Avoid this by adding a new process state flag PS_SWAPPINGIN to a process being swapped in. 3. a running thread being swapped out. Swapout_procs() and swapout() do not check the states of the threads in a process about to be swapped out. This causes the pcb and the kernel stack of a running thread being unmapped, resulting in a page fault in cpu_switch(). Do not swap out a process unless all of its threads are either in a run queue or sleeping. Eventually, it may become our option to swap out only threads that are safe to do so. -- Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> <tanimura@FreeBSD.org> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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