On Mon, 2005-04-18 at 12:52 +0100, Christoph Hellwig wrote: > Oh, I thought the problem is that JFFS2 thought an inode was freed when > it still was in use. So you're problem is actually that it's no in the > hash anymore but you don't know yet? Yes, exactly. VFS developers may always say "it is your problem - redesign JFFS2", but I think it is too late to redesign it.
> Anyway, please explain in detail why you need all this information, what > errors you see, etc so we can find a way to fix it properly. Well, I suspect I explained why I need the mutex. If people will find the explanation vague, I'll make another attempt. The error I see is: Eep. Trying to read_inode #15601 when it's already in state 2! I debugged this a lot before I've realized the reason. And I believe I know JFFS2 very well to claim that redesigning it is very painful. The erroneous code flow is like this: kswapd: removes the inode 15601 from the inode hash (inode.c:478). kswapd: is preempted at inode.c:485 JFFS2 writer: awakes, runs GC to reclaim some space. JFFS2 writer: picks a JFFS2 node belonging to the inode 15601 JFFS2 writer: looks at the inode state, realizes it is in state PRESENT, i.e. it is in the inode cache (which is wrong). JFFS2 writer: runs iget() to acquire a pointer to the struct inode of the inode 15601. JFFS2 writer: iget() calls ->read_inode(), i.e., jffs2_read_inode(). JFFS2 writed: JFFS2 is surprised why read_inode() is called for the already built inode 15601. Or may be VFS is buggy, I'm not sure. May be it shouldn't remove inode from the inode hash in that point (inode.c:487). It sets the I_FREENG state to the inode being freed, and iget() may wait in find_inode_fast() while the inode is actually destroyed (inode.c:562). The inode may be removed from the inode hash later, in dispose_list() (inode.c:292). Or may be this isn't a bug but a feature to make the inode_lock less contended. Not sure, I'm not a VFS guru. In that above described case the code flow would be: kswapd: remove inode 15601 from the inode hash (inode.c:478). kswapd: preempted at inode.s:485 JFFS2 writer: awakes, runs GC to reclaim some space. JFFS2 writer: picks a JFFS2 node belonging to inode 15601 JFFS2 writer: looks at the inode state, realizes it is in state PRESENT, i.e. it is in the inode cache (which is wrong). JFFS2 writer: runs iget() to get the pointer to the struct inode of the inode 15601. JFFS2 writer goes sleep in find_inode_fast(), waiting for freeing completion. kswapd: calls dispose_list(), calls clear_inode() for 15601. JFFS2 writed: read_inode() is called and all is OK since clear_inode() was called before. The latter scenario looks very logical for me. Cheers, Artem. -- Best Regards, Artem B. Bityuckiy, St.-Petersburg, Russia. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
