From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752717AbbATRXj (ORCPT ); Tue, 20 Jan 2015 12:23:39 -0500 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:56964 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751102AbbATRXh (ORCPT ); Tue, 20 Jan 2015 12:23:37 -0500 Message-ID: <1421774615.2080.88.camel@HansenPartnership.com> Subject: Re: module: fix module_refcount() return when running in a module exit routine From: James Bottomley To: Rusty Russell Cc: Masami Hiramatsu , linux-kernel , linux-scsi Date: Tue, 20 Jan 2015 09:23:35 -0800 In-Reply-To: <871tmqcmau.fsf@rustcorp.com.au> 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> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.7 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. James --- diff --git a/include/linux/module.h b/include/linux/module.h index ebfb0e1..b653d7c 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 f191bdd..7b40c5f 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 3965511..63fc779 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -772,9 +772,18 @@ static int try_stop_module(struct module *mod, int flags, int *forced) return 0; } -unsigned long module_refcount(struct module *mod) +/** + * module_refcount - return the refcount or -1 if unloading + * + * @mod: the module we're checking + * + * Returns: + * -1 if the module is in the process of unloading + * otherwise the number of references in the kernel to the module + */ +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 +865,7 @@ 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 +917,7 @@ 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)); } static struct module_attribute modinfo_refcnt =