From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754147Ab0DTJTL (ORCPT ); Tue, 20 Apr 2010 05:19:11 -0400 Received: from ozlabs.org ([203.10.76.45]:37917 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754111Ab0DTJTI (ORCPT ); Tue, 20 Apr 2010 05:19:08 -0400 From: Rusty Russell To: Linus Torvalds Subject: [PATCH] module: drop the lock while waiting for module to complete initialization. Date: Tue, 20 Apr 2010 18:49:04 +0930 User-Agent: KMail/1.12.2 (Linux/2.6.31-19-generic; KDE/4.3.2; i686; ; ) Cc: Brandon Philips , linux-kernel@vger.kernel.org, Herbert Xu , stable@kernel.org MIME-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Message-Id: <201004201849.04960.rusty@rustcorp.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This fixes "gave up waiting for init of module libcrc32c." which happened at boot time due to multiple parallel module loads. The problem was a deadlock: we wait for a module to finish initializing, but we keep the module_lock mutex so it can't complete. In particular, this could reasonably happen if a module does a request_module() in its initialization routine. So we change use_module() to return an errno rather than a bool, and if it's -EBUSY we drop the lock and wait in the caller, then reaquire the lock. Reported-by: Brandon Philips Signed-off-by: Rusty Russell Tested-by: Brandon Philips --- kernel/module.c | 57 +++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 36 insertions(+), 21 deletions(-) diff --git a/kernel/module.c b/kernel/module.c --- a/kernel/module.c +++ b/kernel/module.c @@ -510,33 +510,26 @@ int use_module(struct module *a, struct struct module_use *use; int no_warn, err; - if (b == NULL || already_uses(a, b)) return 1; + if (b == NULL || already_uses(a, b)) + return 0; /* If we're interrupted or time out, we fail. */ - if (wait_event_interruptible_timeout( - module_wq, (err = strong_try_module_get(b)) != -EBUSY, - 30 * HZ) <= 0) { - printk("%s: gave up waiting for init of module %s.\n", - a->name, b->name); - return 0; - } - - /* If strong_try_module_get() returned a different error, we fail. */ + err = strong_try_module_get(b); if (err) - return 0; + return err; DEBUGP("Allocating new usage for %s.\n", a->name); use = kmalloc(sizeof(*use), GFP_ATOMIC); if (!use) { printk("%s: out of memory loading\n", a->name); module_put(b); - return 0; + return -ENOMEM; } use->module_which_uses = a; list_add(&use->list, &b->modules_which_use_me); no_warn = sysfs_create_link(b->holders_dir, &a->mkobj.kobj, a->name); - return 1; + return 0; } EXPORT_SYMBOL_GPL(use_module); @@ -823,7 +816,7 @@ static inline void module_unload_free(st int use_module(struct module *a, struct module *b) { - return strong_try_module_get(b) == 0; + return strong_try_module_get(b); } EXPORT_SYMBOL_GPL(use_module); @@ -994,17 +987,39 @@ static const struct kernel_symbol *resol struct module *owner; const struct kernel_symbol *sym; const unsigned long *crc; + DEFINE_WAIT(wait); + int err; + long timeleft = 30 * HZ; +again: sym = find_symbol(name, &owner, &crc, !(mod->taints & (1 << TAINT_PROPRIETARY_MODULE)), true); - /* use_module can fail due to OOM, - or module initialization or unloading */ - if (sym) { - if (!check_version(sechdrs, versindex, name, mod, crc, owner) - || !use_module(mod, owner)) - sym = NULL; + if (!sym) + return NULL; + + if (!check_version(sechdrs, versindex, name, mod, crc, owner)) + return NULL; + + prepare_to_wait(&module_wq, &wait, TASK_INTERRUPTIBLE); + err = use_module(mod, owner); + if (likely(!err) || err != -EBUSY || signal_pending(current)) { + finish_wait(&module_wq, &wait); + return err ? NULL : sym; } - return sym; + + /* Module is still loading. Drop lock and wait. */ + mutex_unlock(&module_mutex); + timeleft = schedule_timeout(timeleft); + mutex_lock(&module_mutex); + finish_wait(&module_wq, &wait); + + /* Module might be gone entirely, or replaced. Re-lookup. */ + if (timeleft) + goto again; + + printk(KERN_WARNING "%s: gave up waiting for init of module %s.\n", + mod->name, owner->name); + return NULL; } /*