From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [RFC v10][PATCH 08/13] Dump open file descriptors Date: Mon, 01 Dec 2008 09:47:25 -0800 Message-ID: <1228153645.2971.36.camel@nimitz> References: <1227747884-14150-1-git-send-email-orenl@cs.columbia.edu> <1227747884-14150-9-git-send-email-orenl@cs.columbia.edu> <20081128101919.GO28946@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20081128101919.GO28946-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Al Viro Cc: Oren Laadan , Andrew Morton , Linus Torvalds , containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Thomas Gleixner , Serge Hallyn , Ingo Molnar , "H. Peter Anvin" List-Id: linux-api@vger.kernel.org On Fri, 2008-11-28 at 10:19 +0000, Al Viro wrote: > On Wed, Nov 26, 2008 at 08:04:39PM -0500, Oren Laadan wrote: > > +int cr_scan_fds(struct files_struct *files, int **fdtable) > > +{ > > + struct fdtable *fdt; > > + int *fds; > > + int i, n = 0; > > + int tot = CR_DEFAULT_FDTABLE; > > + > > + fds = kmalloc(tot * sizeof(*fds), GFP_KERNEL); > > + if (!fds) > > + return -ENOMEM; > > + > > + /* > > + * We assume that the target task is frozen (or that we checkpoint > > + * ourselves), so we can safely proceed after krealloc() from where > > + * we left off; in the worst cases restart will fail. > > + */ > > Task may be frozen, but it may share the table with any number of other > tasks... First of all, thanks for looking at this, Al. I think Oren's assumption here is that all tasks possibly sharing the table would be frozen. I don't think that's a good assumption, either. :) This would be a lot safer and bulletproof if we size the allocation ahead of time, take all the locks, then retry if the size has changed. I think that will just plain work of we do this: > > + spin_lock(&files->file_lock); > > + rcu_read_lock(); > > + fdt = files_fdtable(files); > > + for (i = 0; i < fdt->max_fds; i++) { > > + if (!fcheck_files(files, i)) > > + continue; > > + if (n == tot) { > > + /* > > + * fcheck_files() is safe with drop/re-acquire > > + * of the lock, because it tests: fd < max_fds > > + */ > > + spin_unlock(&files->file_lock); > > + rcu_read_unlock(); > > + tot *= 2; /* won't overflow: kmalloc will fail */ free(fds); goto first_kmalloc_in_this_function; > > + } > > + fds[n++] = i; > > + } > > + rcu_read_unlock(); > > + spin_unlock(&files->file_lock); > > + > > + *fdtable = fds; > > + return n; > > +} Right? > > + switch (inode->i_mode & S_IFMT) { > > + case S_IFREG: > > + fd_type = CR_FD_FILE; > > + break; > > + case S_IFDIR: > > + fd_type = CR_FD_DIR; > > + break; > > + case S_IFLNK: > > + fd_type = CR_FD_LINK; > > Opened symlinks? May I have whatever you'd been smoking, please? Ugh, that certainly doesn't have any place here. I do wonder if Oren had some use for that in the fully put together code, but it can certainly go for now. I'll send patches for these shortly. -- Dave -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html