Messages in this thread Patch in this message | | | From | Giancarlo Formicuccia <> | Subject | [2.6.13] task_struct->fs_excl, kernel_thread and jffs2 | Date | Thu, 8 Sep 2005 09:47:58 +0200 |
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Hi, [please CC me in any reply] I'm not sure that dup_task_struct() must copy the fs_excl field. This can leads to problems if do_fork() is somehow called while fs_excl!=0. For example, the jffs2 code creates a kernel thread (jffs2_garbage_collect_thread) in a path where lock_super() is held (i.e. by do_remount_sb, during -o remount,rw). When the new thread expires, a badness happens (kernel/exit.c:787). This problem was observed by a couple of people and can be easily reproduced: http://lists.infradead.org/pipermail/linux-mtd/2005-August/013487.html http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2005-September/031109.html
At first glance, I'd simply set fs_excl to 0 for every new thread in dup_task_struct:
--- linux-2.6.13/kernel/fork.c 2005-08-29 01:41:01.000000000 +0200 +++ linux-2.6.13-new/kernel/fork.c 2005-09-07 17:06:23.000000000 +0200 @@ -173,6 +173,7 @@ static struct task_struct *dup_task_stru *tsk = *orig; tsk->thread_info = ti; ti->task = tsk; + atomic_set(&tsk->fs_excl, 0); /* One for us, one for whoever does the "release_task()" (usually parent) */ atomic_set(&tsk->usage,2); but I've a doubt about the WARN_ON in exit.c being actually here to report these kernel_thread() users (like jffs2)...
Any comment/suggestion?
Thanks,
Giancarlo
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