On Friday 09 March 2007 09:14, Pekka J Enberg wrote: > From: Pekka Enberg <[EMAIL PROTECTED]> > > This adds a f_light flag to struct file to indicate that the file was > looked up with fget_light(). Needed by revoke to ensure we don't > close a file pointer while someone is using it without actually > holding a reference. > > These bits were taken from the forced unmount patches by Tigran > Aivazian.
Well, I disagree very much with this patch. One of the interest of fget_light() is not dirtying file structure (avoiding atomic changes to f_count). You add a 'flag' (4 bytes !) at the end of the file structure (so in a different cache line than the parts that are usually accessed in a fd_related syscall) and dirty this part at syscall entry and exit. Thats really a heavy price for supporting an unlikely revoke() syscall. Also, the thing is racy. ( BTW, the whole revoke() concept is evil, especially if we want to avoid using inodes/dentries for some kind of pseudo files like sockets / pipes) Cannot we use a flag in 'struct files_struct', set to one when the task is mono-thread (at task creation in fact), and set to 0 when it creates a new thread (or when someone remotely access to this "struct files_struct" in /proc/pid/fd/... ) No need to set back this flag to 1 when task revert to mono-threaded, since this case is probably unlikely. This way we can be non racy. - 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/