Le Tue, 24 Jul 2007 14:28:05 +0100, Al Viro <[EMAIL PROTECTED]> a écrit :
>On Tue, Jul 24, 2007 at 01:57:53PM +0200, Alban Crequy wrote: >> Hi, >> >> I have a problem with the error management of add_disk() and >> del_gendisk(). >> >> add_disk() adds an entry in /sys/block/<name>. The filename >> in /sys/block is not (struct gen_disk)->disk_name but more or less >> the first KOBJ_NAME_LEN characters of (struct gen_disk)->disk_name. >> >> #define KOBJ_NAME_LEN 20 >> >> My problem occurs when we try to add 2 disks with different names, >> but when the KOBJ_NAME_LEN first characters are the same. > >So don't do that. I no more do that. But I still think it would be better if we found a way to manage errors in that case. I fear that parts of kernel make this error. For example, old version of GFS has this code: http://csourcesearch.net/package/gfs-kernel/2.6.9/gfs-kernel-2.6.9-27/src/gfs/diaper.c char buf[BDEVNAME_SIZE]; bdevname(real, buf); snprintf(gd->disk_name, sizeof(gd->disk_name), "diapered_%s", buf); Since BDEVNAME_SIZE is 32 and KOBJ_NAME_LEN is 20, the bug happens quite easily. I did not check closely if this is a problem, but there is other parts in the current kernel that build the disk_name with snprintf("...%s...") >> The attached test module triggers the problem. You can try something >> like: for i in $(seq 1 100) ; do insmod ./adddiskbug.ko ; rmmod >> adddiskbug ; done >> >> The attached patch fixes the problem by changing the prototype of >> add_disk() and register_disk() to return errors. > >This is bogus. Just what would callers do with these error values? >Ignore them silently? Bail out? Can't do - at that point disk just >might have been opened already. add_disk() is the point of no return; >we are already past the last point where we could bail out. I missed that point - that the disk might have been opened. Where is the point of no return in add_disk() exactly? Is it really before the kobject_add() that causes the problem? In this case, perhaps we can 1/ check that the kobject_add() will not fail before the point of no return, 2/ pass this point and then 3/ do the kobject_add(). And add appropriate locking to ensure that nobody add another disk with the same 20-characters truncated name between 1/ and 3/. - 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/
