From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753286AbbAVQuY (ORCPT ); Thu, 22 Jan 2015 11:50:24 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:39708 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753179AbbAVQuV (ORCPT ); Thu, 22 Jan 2015 11:50:21 -0500 Date: Thu, 22 Jan 2015 08:50:18 -0800 From: Christoph Hellwig To: James Bottomley Cc: Rusty Russell , Masami Hiramatsu , linux-kernel , linux-scsi Subject: Re: module: fix module_refcount() return when running in a module exit routine Message-ID: <20150122165018.GA27377@infradead.org> References: <1421600146.2080.8.camel@HansenPartnership.com> <54BC93C3.7010808@hitachi.com> <878ugzco8c.fsf@rustcorp.com.au> <1421683701.2080.25.camel@HansenPartnership.com> <871tmqcmau.fsf@rustcorp.com.au> <1421774615.2080.88.camel@HansenPartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1421774615.2080.88.camel@HansenPartnership.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 20, 2015 at 09:23:35AM -0800, James Bottomley wrote: > On Tue, 2015-01-20 at 11:15 +1030, Rusty Russell wrote: > > James Bottomley writes: > > > On Mon, 2015-01-19 at 16:21 +1030, Rusty Russell wrote: > > >> Masami Hiramatsu writes: > > >> > (2015/01/19 1:55), James Bottomley wrote: > > >> >> From: James Bottomley > > >> >> > > >> >> After e513cc1 module: Remove stop_machine from module unloading, > > >> >> module_refcount() is returning (unsigned long)-1 when called from within > > >> >> a routine that runs in module_exit. This is confusing the scsi device > > >> >> put code which is coded to detect a module_refcount() of zero for > > >> >> running within a module exit routine and not try to do another > > >> >> module_put. The fix is to restore the original behaviour of > > >> >> module_refcount() and return zero if we're running inside an exit > > >> >> routine. > > >> >> > > >> >> Fixes: e513cc1c07e2ab93a4514eec9833e031df3e30bb > > >> >> Reported-by: Bart Van Assche > > >> >> Signed-off-by: James Bottomley > > >> >> > > >> > > > >> > Yes, this should be fixed as you said, since it must return "unsigned long" value. > > >> > > >> But there are only three non-module callers: > > >> > > >> drivers/scsi/scsi.c:1012: if (module && module_refcount(module) != 0) > > >> drivers/staging/lustre/lustre/obdclass/lu_object.c:1359: LINVRNT(module_refcount(key->lct_owner) > 0); > > >> include/linux/module.h:447:unsigned long module_refcount(struct module *mod); > > >> kernel/debug/kdb/kdb_main.c:2026: kdb_printf("%4ld ", module_refcount(mod)); > > >> kernel/module.c:775:unsigned long module_refcount(struct module *mod) > > >> kernel/module.c:779:EXPORT_SYMBOL(module_refcount); > > >> kernel/module.c:859: seq_printf(m, " %lu ", module_refcount(mod)); > > >> kernel/module.c:911: return sprintf(buffer, "%lu\n", module_refcount(mk->mod)); > > >> > > >> The first one I think should be eliminated, and the second one is simply > > >> an assertion before calling module_put() (which should probably be > > >> eliminated). The others are just printing information. > > > > > > If you really want to insist on module_reference() returning -1 when the > > > module is in it's exit phase, OK, but in that case, I think it should > > > return a signed value, not an unsigned one. > > > > Sure; I just didn't want to paper over the problem here. And I'm not > > sure we want to lose information, eg. in kgdb we're presumably looking > > at it because something went wrong... > > > > Thanks, > > Rusty. > > > > Subject: module: make module_refcount() a signed integer. > > > > James Bottomley points out that it will be -1 during unload. It's > > only used for diagnostics, so let's not hide that as it could be a > > clue as to what's gone wrong. > > > > Cc: Jason Wessel > > Signed-off-by: Rusty Russell > > > > diff --git a/include/linux/module.h b/include/linux/module.h > > index ebfb0e153c6a..b653d7c0a05a 100644 > > --- a/include/linux/module.h > > +++ b/include/linux/module.h > > @@ -444,7 +444,7 @@ extern void __module_put_and_exit(struct module *mod, long code) > > #define module_put_and_exit(code) __module_put_and_exit(THIS_MODULE, code) > > > > #ifdef CONFIG_MODULE_UNLOAD > > -unsigned long module_refcount(struct module *mod); > > +int module_refcount(struct module *mod); > > void __symbol_put(const char *symbol); > > #define symbol_put(x) __symbol_put(VMLINUX_SYMBOL_STR(x)) > > void symbol_put_addr(void *addr); > > diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c > > index f191bddf64b8..7b40c5f07dce 100644 > > --- a/kernel/debug/kdb/kdb_main.c > > +++ b/kernel/debug/kdb/kdb_main.c > > @@ -2023,7 +2023,7 @@ static int kdb_lsmod(int argc, const char **argv) > > kdb_printf("%-20s%8u 0x%p ", mod->name, > > mod->core_size, (void *)mod); > > #ifdef CONFIG_MODULE_UNLOAD > > - kdb_printf("%4ld ", module_refcount(mod)); > > + kdb_printf("%4d ", module_refcount(mod)); > > #endif > > if (mod->state == MODULE_STATE_GOING) > > kdb_printf(" (Unloading)"); > > diff --git a/kernel/module.c b/kernel/module.c > > index 3965511ae133..2387c98347c1 100644 > > --- a/kernel/module.c > > +++ b/kernel/module.c > > @@ -772,9 +772,9 @@ static int try_stop_module(struct module *mod, int flags, int *forced) > > return 0; > > } > > > > -unsigned long module_refcount(struct module *mod) > > +int module_refcount(struct module *mod) > > { > > - return (unsigned long)atomic_read(&mod->refcnt) - MODULE_REF_BASE; > > + return atomic_read(&mod->refcnt) - MODULE_REF_BASE; > > } > > EXPORT_SYMBOL(module_refcount); > > > > @@ -856,7 +856,7 @@ static inline void print_unload_info(struct seq_file *m, struct module *mod) > > struct module_use *use; > > int printed_something = 0; > > > > - seq_printf(m, " %lu ", module_refcount(mod)); > > + seq_printf(m, " %i ", module_refcount(mod)); > > > > /* > > * Always include a trailing , so userspace can differentiate > > @@ -908,7 +908,7 @@ EXPORT_SYMBOL_GPL(symbol_put_addr); > > static ssize_t show_refcnt(struct module_attribute *mattr, > > struct module_kobject *mk, char *buffer) > > { > > - return sprintf(buffer, "%lu\n", module_refcount(mk->mod)); > > + return sprintf(buffer, "%i\n", module_refcount(mk->mod)); > > } > > Actually, I don't think this is enough. Some Australian once came up > with a guide to APIs, and lectured on it at length, one of which was > that the name should be the obvious use and it is unexpected that a > refcount would go negative. I think we could raise it from -6 on the > API scale to +3 if we add some documentation like below. We'll also still need to change scsi_device_put to deal with a negative refcount..