Feature #3239
open008: Driver becomes not available for unloading permanently
0%
Description
(copied almost as is from kernel-rules/rules/DRVRULES_en.trl)
SUMMARY¶
Once you blocked a driver using `try_module_get()` you should unblock it by `module_put()`.
DESCRIPTION¶
There is a possibility to block unloading of a driver (kernel module). You might want to use it if the driver is currently in use by OS objects or user processes. However, its uncautious usage can undermine stability of the system as a whole.
Note that such calls can be nested (they increase/decrease semaphore counter internally). Therefore, you should call exactly one proceure that unblocks the driver for each preceeding blocking one. Otherwise, the driver will not be available for unloading--without any serious reason to put such a restriction.
LINKS¶
[Sample bugfix](http://lkml.org/lkml/2010/1/12/246) of `drivers/mtd/mtd_blkdevs.c`
EXAMPLE¶
Sample error:
static int dev_open(struct inode*, struct file*) { try_module_get(THIS_MODULE); ... //the absence of the module_put(THIS_MODULE) call return 0; }
Sample error in `drivers/mtd/mtd_blkdevs.c`:
static int blktrans_open(struct block_device *bdev, fmode_t mode) { struct mtd_blktrans_dev *dev = bdev->bd_disk->private_data; struct mtd_blktrans_ops *tr = dev->tr; int ret = -ENODEV; if (!get_mtd_device(NULL, dev->mtd->index)) goto out; if (!try_module_get(tr->owner)) goto out_tr; /* FIXME: Locking. A hot pluggable device can go away (del_mtd_device can be called for it) without its module being unloaded. */ dev->mtd->usecount++; ret = 0; if (tr->open && (ret = tr->open(dev))) { dev->mtd->usecount--; put_mtd_device(dev->mtd); out_tr: module_put(tr->owner); } out: return ret; }
1. If `try_module_get(tr->owner) == 0` then we goto label `out_tr`;
2. At label `out_tr` we call `module_put` on the unloaded driver;
To fix the error we should replace:
goto out_tr;
with
goto out;
Updated by Ilya Shchepetkov over 12 years ago
- Subject changed from 008: Driver becomes not available for unloading permanently to 08_1: Driver becomes not available for unloading permanently
- Status changed from New to Resolved
Fixed in commit d83e232 of fix_08_1a branch. Will be merged to master together with it.
Updated by Alexey Khoroshilov over 11 years ago
- Subject changed from 08_1: Driver becomes not available for unloading permanently to 008_1: Driver becomes not available for unloading permanently
Updated by Vadim Mutilin almost 11 years ago
- Subject changed from 008_1: Driver becomes not available for unloading permanently to 008: Driver becomes not available for unloading permanently
Updated by Evgeny Novikov almost 11 years ago
- Status changed from Resolved to Open
Commit 762fb1d to the main kernel Makefile in particular has added "-Werror=strict-prototypes" to CFLAGS. This causes an error for function prototype:
extern void ldv_module_put_and_exit();
Updated by Evgeny Novikov over 10 years ago
- Status changed from Open to Resolved
- Assignee deleted (
Ilya Shchepetkov)
The issue was fixed in 661eeff9 by Vladimir.