linux-kernel - Re: kmod: provide wrappers for kmod

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Date:   Wed, 21 Dec 2016 21:07:21 -0800
From:   Jessica Yu <jeyu@...hat.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     shuah@...nel.org, rusty@...tcorp.com.au, ebiederm@...ssion.com,
        dmitry.torokhov@...il.com, acme@...hat.com, corbet@....net,
        martin.wilck@...e.com, mmarek@...e.com, pmladek@...e.com,
        hare@...e.com, rwright@....com, jeffm@...e.com, DSterba@...e.com,
        fdmanana@...e.com, neilb@...e.com, linux@...ck-us.net,
        rgoldwyn@...e.com, subashab@...eaurora.org, xypron.glpk@....de,
        keescook@...omium.org, atomlin@...hat.com, mbenes@...e.cz,
        paulmck@...ux.vnet.ibm.com, dan.j.williams@...el.com,
        jpoimboe@...hat.com, davem@...emloft.net, mingo@...hat.com,
        akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
        linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: kmod: provide wrappers for kmod_concurrent inc/dec

+++ Luis R. Rodriguez [08/12/16 11:48 -0800]:
>kmod_concurrent is used as an atomic counter for enabling
>the allowed limit of modprobe calls, provide wrappers for it
>to enable this to be expanded on more easily. This will be done
>later.
>
>Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
>---
> kernel/kmod.c | 27 +++++++++++++++++++++------
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
>diff --git a/kernel/kmod.c b/kernel/kmod.c
>index cb6f7ca7b8a5..049d7eabda38 100644
>--- a/kernel/kmod.c
>+++ b/kernel/kmod.c
>@@ -44,6 +44,9 @@
> #include <trace/events/module.h>
>
> extern int max_threads;
>+
>+static atomic_t kmod_concurrent = ATOMIC_INIT(0);
>+
> unsigned int max_modprobes;
> module_param(max_modprobes, uint, 0644);
> MODULE_PARM_DESC(max_modprobes, "Max number of allowed concurrent modprobes");
>@@ -108,6 +111,20 @@ static int call_modprobe(char *module_name, int wait)
> 	return -ENOMEM;
> }
>
>+static int kmod_umh_threads_get(void)
>+{
>+	atomic_inc(&kmod_concurrent);
>+	if (atomic_read(&kmod_concurrent) < max_modprobes)

Should this not be <=? I think this only allows up to max_modprobes-1 concurrent threads.

>+		return 0;
>+	atomic_dec(&kmod_concurrent);
>+	return -ENOMEM;
>+}
>+
>+static void kmod_umh_threads_put(void)
>+{
>+	atomic_dec(&kmod_concurrent);
>+}
>+
> /**
>  * __request_module - try to load a kernel module
>  * @wait: wait (or not) for the operation to complete
>@@ -129,7 +146,6 @@ int __request_module(bool wait, const char *fmt, ...)
> 	va_list args;
> 	char module_name[MODULE_NAME_LEN];
> 	int ret;
>-	static atomic_t kmod_concurrent = ATOMIC_INIT(0);
> 	static int kmod_loop_msg;
>
> 	/*
>@@ -153,8 +169,8 @@ int __request_module(bool wait, const char *fmt, ...)
> 	if (ret)
> 		return ret;
>
>-	atomic_inc(&kmod_concurrent);
>-	if (atomic_read(&kmod_concurrent) > max_modprobes) {
>+	ret = kmod_umh_threads_get();
>+	if (ret) {
> 		/* We may be blaming an innocent here, but unlikely */
> 		if (kmod_loop_msg < 5) {
> 			printk(KERN_ERR
>@@ -162,15 +178,14 @@ int __request_module(bool wait, const char *fmt, ...)
> 			       module_name);
> 			kmod_loop_msg++;
> 		}
>-		atomic_dec(&kmod_concurrent);
>-		return -ENOMEM;
>+		return ret;
> 	}
>
> 	trace_module_request(module_name, wait, _RET_IP_);
>
> 	ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
>
>-	atomic_dec(&kmod_concurrent);
>+	kmod_umh_threads_put();
> 	return ret;
> }
> EXPORT_SYMBOL(__request_module);
>-- 
>2.10.1
>