Re: [PATCH] block: break circular locks in blk_request_module
From: Christoph Hellwig <hch@infradead.org>
Date: 2021-06-17 11:52:03
Also in:
linux-block, lkml
Subsystem:
memory technology devices (mtd), the rest · Maintainers:
Miquel Raynal, Richard Weinberger, Vignesh Raghavendra, Linus Torvalds
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; }
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