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SubjectRe: Patch/resubmit linux-2.5.63-bk4 try_module_get simplification
The patch below was included by Linus around 2/14/03.

On Fri, Mar 07, 2003 at 05:34:18PM +1100, Rusty Russell wrote:
> Three other requests, if I may.
>
> It'd be nice to have a comment for the two smp_mb() eg. /* Must increment
> before checking state */ and vice-versa above the one in module.c. Secondly
> probably nicer to just rename the modlist_lock to module_lock and use that,
> and thirdly merge with the racefix patch below if Linus hasn't already
> taken it.
>
>
> Name: Fix two module races
> Author: Bob Miller, Rusty Russell
> Status: Trivial
>
> D: Bob Miller points out that the try_module_get in use_module() can,
> D: of course, fail. Secondly, there is a race between setting the module
> D: live, and a simultaneous removal of it.
>
> diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.62-bk6/kernel/module.c working-2.5.62-bk6-modraces/kernel/module.c
> --- linux-2.5.62-bk6/kernel/module.c 2003-02-18 11:18:57.000000000 +1100
> +++ working-2.5.62-bk6-modraces/kernel/module.c 2003-02-24 13:42:44.000000000 +1100
> @@ -173,16 +173,19 @@ static int use_module(struct module *a,
> struct module_use *use;
> if (b == NULL || already_uses(a, b)) return 1;
>
> + if (!strong_try_module_get(b))
> + return 0;
> +
> 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;
> }
>
> use->module_which_uses = a;
> list_add(&use->list, &b->modules_which_use_me);
> - try_module_get(b); /* Can't fail */
> return 1;
> }
>
> @@ -1456,10 +1459,12 @@ sys_init_module(void *umod,
> }
>
> /* Now it's a first class citizen! */
> + down(&module_mutex);
> mod->state = MODULE_STATE_LIVE;
> module_free(mod, mod->module_init);
> mod->module_init = NULL;
> mod->init_size = 0;
> + up(&module_mutex);
>
> return 0;
> }
>

--
Bob Miller Email: rem@osdl.org
Open Source Development Lab Phone: 503.626.2455 Ext. 17
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