On Thu, 20 Jan 2011, Christoph Hellwig wrote: > On Thu, Jan 20, 2011 at 01:30:58PM +0100, Miklos Szeredi wrote: > > From: Miklos Szeredi <mszeredi@xxxxxxx> > > > > Running a fuse filesystem with multiple open()'s in parallel can > > trigger a "kernel BUG at mm/truncate.c:475" > > > > The reason is, unmap_mapping_range() is not prepared for more than > > one concurrent invocation per inode. For example: > > > > thread1: going through a big range, stops in the middle of a vma and > > stores the restart address in vm_truncate_count. > > > > thread2: comes in with a small (e.g. single page) unmap request on > > the same vma, somewhere before restart_address, finds that the > > vma was already unmapped up to the restart address and happily > > returns without doing anything. > > > > Another scenario would be two big unmap requests, both having to > > restart the unmapping and each one setting vm_truncate_count to its > > own value. This could go on forever without any of them being able to > > finish. > > > > Truncate and hole punching already serialize with i_mutex. Other > > callers of unmap_mapping_range() do not, and it's difficult to get > > i_mutex protection for all callers. In particular ->d_revalidate(), > > which calls invalidate_inode_pages2_range() in fuse, may be called > > with or without i_mutex. > > > Which I think is mostly a fuse problem. I really hate bloating the > generic inode (into which the address_space is embedded) with another > mutex for deficits in rather special case filesystems. As Hugh pointed out unmap_mapping_range() has grown a varied set of callers, which are difficult to fix up wrt i_mutex. Fuse was just an example. I don't like the bloat either, but this is the best I could come up with for fixing this problem generally. If you have a better idea, please share it. Thanks, Miklos -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>