From: Christoph Hellwig <hch@infradead.org>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, skhan@linuxfoundation.org,
gregkh@linuxfoundation.org,
linux-kernel-mentees@lists.linuxfoundation.org,
syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com,
miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com,
linux-mtd@lists.infradead.org
Subject: Re: [PATCH] block: break circular locks in blk_request_module
Date: Thu, 17 Jun 2021 12:51:23 +0100 [thread overview]
Message-ID: <YMs3O/cg4V7ywlVq@infradead.org> (raw)
In-Reply-To: <20210617092016.522985-1-desmondcheongzx@gmail.com>
On Thu, Jun 17, 2021 at 05:20:16PM +0800, Desmond Cheong Zhi Xi wrote:
> mutex_lock(&major_names_lock);
> for (n = &major_names[major_to_index(major)]; *n; n = &(*n)->next) {
> if ((*n)->major == major && (*n)->probe) {
> - (*n)->probe(devt);
> + probe = (*n)->probe;
> mutex_unlock(&major_names_lock);
> + probe(devt);
And now you can all probe after it has been freed and/or the module has
been unloaded. The obviously correct fix is to only hold mtd_table_mutex
for the actually required critical section:
diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index fb8e12d590a1..065d94f9b1fb 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -529,13 +529,11 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
register_mtd_user(&blktrans_notifier);
- mutex_lock(&mtd_table_mutex);
ret = register_blkdev(tr->major, tr->name);
if (ret < 0) {
printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
tr->name, tr->major, ret);
- mutex_unlock(&mtd_table_mutex);
return ret;
}
@@ -545,12 +543,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
tr->blkshift = ffs(tr->blksize) - 1;
INIT_LIST_HEAD(&tr->devs);
- list_add(&tr->list, &blktrans_majors);
+ mutex_lock(&mtd_table_mutex);
+ list_add(&tr->list, &blktrans_majors);
mtd_for_each_device(mtd)
if (mtd->type != MTD_ABSENT)
tr->add_mtd(tr, mtd);
-
mutex_unlock(&mtd_table_mutex);
return 0;
}
next prev parent reply other threads:[~2021-06-17 11:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-17 9:20 [PATCH] block: break circular locks in blk_request_module Desmond Cheong Zhi Xi
2021-06-17 11:51 ` Christoph Hellwig [this message]
2021-06-17 15:23 ` Desmond Cheong Zhi Xi
2021-06-17 15:27 ` Christoph Hellwig
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