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Date: Wed, 2 May 2018 09:34:03 +0200
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Eric Biggers <ebiggers3@...il.com>,
syzbot+4684a000d5abdade83fac55b1e7d1f935ef1936e@...kaller.appspotmail.com,
Jens Axboe <axboe@...nel.dk>,
LKML <linux-kernel@...r.kernel.org>,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: possible deadlock in blkdev_reread_part
/\/\/\/\/\/\On Fri, Apr 20, 2018 at 4:06 PM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
> Tetsuo Handa wrote:
>> Eric Biggers wrote:
>> > It seems that ->bd_mutex is held while opening and closing block devices, which
>> > should rank it above both ->lo_ctl_mutex and loop_index_mutex (see lo_open() and
>> > lo_release()).
>> >
>> > But blkdev_reread_part(), which takes ->bd_mutex, is called from some of the
>> > ioctls while ->lo_ctl_mutex is held.
>> >
>> > Perhaps we should call blkdev_reread_part() at the end of the ioctls, after
>> > ->lo_ctl_mutex has been dropped? But it looks like that can do I/O to the
>> > device, which probably could race with loop_clr_fd()...
>> >
>> > Or perhaps we should just take both locks for the ioctls, in the order
>> > ->bd_mutex, then ->lo_ctl_mutex -- and then use __blkdev_reread_part()?
>>
>> But do we really need ->lo_ctl_mutex ? What is the purpose of ->lo_ctl_mutex ?
>> If the purpose of ->lo_ctl_mutex is to serialize ioctl() request against each
>> loop device when multiple threads opened the same loop device, I feel that
>>
>> There is no need to use ->lo_ctl_mutex which the lockdep will check and
>> complain, provided that ioctl() request cannot recurse into ioctl() request.
>> Instead, we can use simple flag variable whether an ioctl() is in progress.
>>
>> There is no need to use ->lo_ctl_mutex from __lo_release(), for it is
>> guaranteed that there is no in-flight ioctl() request when __lo_release()
>> is called, and loop_index_mutex is blocking further open() requests.
>>
>> and simplify like below.
>>
> Can we test this patch?
>
> >From 0ca0694b74ca4b02e9d2e3f46c9d960ba167adec Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Fri, 20 Apr 2018 22:54:42 +0900
> Subject: [PATCH] block/loop: Serialize ioctl operations.
>
> syzbot is reporting various bugs which involve /dev/loopX.
> Two of them
>
> INFO: rcu detected stall in lo_ioctl
> https://syzkaller.appspot.com/bug?id=7b49fb610af9cca78c24e9f796f2e8b0d5573997
>
> general protection fault in lo_ioctl (2)
> https://syzkaller.appspot.com/bug?id=f3cfe26e785d85f9ee259f385515291d21bd80a3
/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
Now there is a repro for this one. I've pushed it to kernel mailing lists:
https://groups.google.com/d/msg/syzkaller-bugs/c8KUcTAzTvA/3o_7g6-tAwAJ
> suggest that loop module is not thread safe. The former suggests that
> l->lo_backing_file is forming circular loop and the latter suggests that
> l->lo_backing_file became NULL.
>
> In fact, recursion avoidance check in loop_set_fd() is traversing loop
> devices without holding each lo->lo_ctl_mutex lock. lo_state can become
> Lo_rundown and lo_backing_file can become NULL if raced with loop_clr_fd().
>
> /* Avoid recursion */
> f = file;
> while (is_loop_device(f)) {
> struct loop_device *l;
>
> if (f->f_mapping->host->i_bdev == bdev)
> goto out_putf;
>
> l = f->f_mapping->host->i_bdev->bd_disk->private_data;
> if (l->lo_state == Lo_unbound) {
> error = -EINVAL;
> goto out_putf;
> }
> f = l->lo_backing_file;
> }
>
> Since ioctl() request on loop devices is not frequent operation, we don't
> need fine grained locking. Let's use global lock rather than dancing with
> locking order inside this recursion avoidance check.
>
> Strategy is that the global lock is held upon entry of ioctl() request,
> and release it before either starting operations which might recurse or
> leaving ioctl() request. After the global lock is released, current thread
> no longer uses "struct loop_device" memory because it might be modified
> by next ioctl() request which was waiting for current ioctl() request.
>
> In order to enforce this strategy, this patch inversed
> loop_reread_partitions() and loop_unprepare_queue() in loop_clr_fd().
> I don't know whether it breaks something, but I don't have testcases.
>
> Since this patch serializes using global lock, race bugs should no longer
> exist. Thus, it will be easy to test whether this patch broke something.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+e5e426c6a47c26ada908348fe84aff916a26d337@...kaller.appspotmail.com>
> Reported-by: syzbot <syzbot+116e7de10c6752bf5e1e@...kaller.appspotmail.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> ---
> drivers/block/loop.c | 231 ++++++++++++++++++++++++++++-----------------------
> drivers/block/loop.h | 1 -
> 2 files changed, 128 insertions(+), 104 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index c9d0449..59716d1 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -81,11 +81,50 @@
> #include <linux/uaccess.h>
>
> static DEFINE_IDR(loop_index_idr);
> -static DEFINE_MUTEX(loop_index_mutex);
> +static DEFINE_MUTEX(loop_mutex);
> +static void *loop_mutex_owner; /* == __mutex_owner(&loop_mutex) */
>
> static int max_part;
> static int part_shift;
>
> +/*
> + * lock_loop - Lock loop_mutex.
> + */
> +static void lock_loop(void)
> +{
> + mutex_lock(&loop_mutex);
> + loop_mutex_owner = current;
> +}
> +
> +/*
> + * lock_loop_killable - Lock loop_mutex unless killed.
> + */
> +static int lock_loop_killable(void)
> +{
> + int err = mutex_lock_killable(&loop_mutex);
> +
> + if (err)
> + return err;
> + loop_mutex_owner = current;
> + return 0;
> +}
> +
> +/*
> + * unlock_loop - Unlock loop_mutex as needed.
> + *
> + * Explicitly call this function before calling fput() or blkdev_reread_part()
> + * in order to avoid circular lock dependency. After this function is called,
> + * current thread is no longer allowed to access "struct loop_device" memory,
> + * for another thread would access that memory as soon as loop_mutex is held.
> + */
> +static void unlock_loop(void)
> +{
> + if (loop_mutex_owner == current) {
> + loop_mutex_owner = NULL;
> + mutex_unlock(&loop_mutex);
> + }
> +}
> +
> static int transfer_xor(struct loop_device *lo, int cmd,
> struct page *raw_page, unsigned raw_off,
> struct page *loop_page, unsigned loop_off,
> @@ -604,7 +643,12 @@ static void loop_reread_partitions(struct loop_device *lo,
> struct block_device *bdev)
> {
> int rc;
> + /* Save variables which might change after unlock_loop() is called. */
> + char filename[sizeof(lo->lo_file_name)];
> + const int num = lo->lo_number;
>
> + memmove(filename, lo->lo_file_name, sizeof(filename));
> + unlock_loop();
> /*
> * bd_mutex has been held already in release path, so don't
> * acquire it if this function is called in such case.
> @@ -619,7 +663,7 @@ static void loop_reread_partitions(struct loop_device *lo,
> rc = blkdev_reread_part(bdev);
> if (rc)
> pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
> - __func__, lo->lo_number, lo->lo_file_name, rc);
> + __func__, num, filename, rc);
> }
>
> /*
> @@ -637,6 +681,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
> struct inode *inode;
> int error;
>
> + lockdep_assert_held(&loop_mutex);
> error = -ENXIO;
> if (lo->lo_state != Lo_bound)
> goto out;
> @@ -673,12 +718,14 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
> loop_update_dio(lo);
> blk_mq_unfreeze_queue(lo->lo_queue);
>
> - fput(old_file);
> if (lo->lo_flags & LO_FLAGS_PARTSCAN)
> - loop_reread_partitions(lo, bdev);
> + loop_reread_partitions(lo, bdev); /* calls unlock_loop() */
> + unlock_loop();
> + fput(old_file);
> return 0;
>
> out_putf:
> + unlock_loop();
> fput(file);
> out:
> return error;
> @@ -862,6 +909,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
> int error;
> loff_t size;
>
> + lockdep_assert_held(&loop_mutex);
> /* This is safe, since we have a reference from open(). */
> __module_get(THIS_MODULE);
>
> @@ -936,19 +984,21 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
> set_blocksize(bdev, S_ISBLK(inode->i_mode) ?
> block_size(inode->i_bdev) : PAGE_SIZE);
>
> + /*
> + * Grab the block_device to prevent its destruction after we
> + * put /dev/loopXX inode. Later in loop_clr_fd() we bdput(bdev).
> + */
> + bdgrab(bdev);
> +
> lo->lo_state = Lo_bound;
> if (part_shift)
> lo->lo_flags |= LO_FLAGS_PARTSCAN;
> if (lo->lo_flags & LO_FLAGS_PARTSCAN)
> - loop_reread_partitions(lo, bdev);
> -
> - /* Grab the block_device to prevent its destruction after we
> - * put /dev/loopXX inode. Later in loop_clr_fd() we bdput(bdev).
> - */
> - bdgrab(bdev);
> + loop_reread_partitions(lo, bdev); /* calls unlock_loop() */
> return 0;
>
> out_putf:
> + unlock_loop();
> fput(file);
> out:
> /* This is safe: open() is still holding a reference. */
> @@ -998,7 +1048,9 @@ static int loop_clr_fd(struct loop_device *lo)
> struct file *filp = lo->lo_backing_file;
> gfp_t gfp = lo->old_gfp_mask;
> struct block_device *bdev = lo->lo_device;
> + bool reread;
>
> + lockdep_assert_held(&loop_mutex);
> if (lo->lo_state != Lo_bound)
> return -ENXIO;
>
> @@ -1014,7 +1066,6 @@ static int loop_clr_fd(struct loop_device *lo)
> */
> if (atomic_read(&lo->lo_refcnt) > 1) {
> lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
> - mutex_unlock(&lo->lo_ctl_mutex);
> return 0;
> }
>
> @@ -1059,20 +1110,14 @@ static int loop_clr_fd(struct loop_device *lo)
> /* This is safe: open() is still holding a reference. */
> module_put(THIS_MODULE);
> blk_mq_unfreeze_queue(lo->lo_queue);
> -
> - if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
> - loop_reread_partitions(lo, bdev);
> + reread = (lo->lo_flags & LO_FLAGS_PARTSCAN) && bdev;
> lo->lo_flags = 0;
> if (!part_shift)
> lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
> loop_unprepare_queue(lo);
> - mutex_unlock(&lo->lo_ctl_mutex);
> - /*
> - * Need not hold lo_ctl_mutex to fput backing file.
> - * Calling fput holding lo_ctl_mutex triggers a circular
> - * lock dependency possibility warning as fput can take
> - * bd_mutex which is usually taken before lo_ctl_mutex.
> - */
> + if (reread)
> + loop_reread_partitions(lo, bdev); /* calls unlock_loop() */
> + unlock_loop();
> fput(filp);
> return 0;
> }
> @@ -1162,7 +1207,7 @@ static int loop_clr_fd(struct loop_device *lo)
> !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
> lo->lo_flags |= LO_FLAGS_PARTSCAN;
> lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
> - loop_reread_partitions(lo, lo->lo_device);
> + loop_reread_partitions(lo, lo->lo_device); /* calls unlock_loop() */
> }
>
> return err;
> @@ -1171,14 +1216,13 @@ static int loop_clr_fd(struct loop_device *lo)
> static int
> loop_get_status(struct loop_device *lo, struct loop_info64 *info)
> {
> - struct file *file;
> + struct path path;
> struct kstat stat;
> int ret;
>
> - if (lo->lo_state != Lo_bound) {
> - mutex_unlock(&lo->lo_ctl_mutex);
> + lockdep_assert_held(&loop_mutex);
> + if (lo->lo_state != Lo_bound)
> return -ENXIO;
> - }
>
> memset(info, 0, sizeof(*info));
> info->lo_number = lo->lo_number;
> @@ -1195,17 +1239,17 @@ static int loop_clr_fd(struct loop_device *lo)
> lo->lo_encrypt_key_size);
> }
>
> - /* Drop lo_ctl_mutex while we call into the filesystem. */
> - file = get_file(lo->lo_backing_file);
> - mutex_unlock(&lo->lo_ctl_mutex);
> - ret = vfs_getattr(&file->f_path, &stat, STATX_INO,
> - AT_STATX_SYNC_AS_STAT);
> + /* Drop loop_mutex while we call into the filesystem. */
> + path = lo->lo_backing_file->f_path;
> + path_get(&path);
> + unlock_loop();
> + ret = vfs_getattr(&path, &stat, STATX_INO, AT_STATX_SYNC_AS_STAT);
> if (!ret) {
> info->lo_device = huge_encode_dev(stat.dev);
> info->lo_inode = stat.ino;
> info->lo_rdevice = huge_encode_dev(stat.rdev);
> }
> - fput(file);
> + path_put(&path);
> return ret;
> }
>
> @@ -1267,6 +1311,7 @@ static int loop_clr_fd(struct loop_device *lo)
> struct loop_info info;
> struct loop_info64 info64;
>
> + lockdep_assert_held(&loop_mutex);
> if (copy_from_user(&info, arg, sizeof (struct loop_info)))
> return -EFAULT;
> loop_info64_from_old(&info, &info64);
> @@ -1278,6 +1323,7 @@ static int loop_clr_fd(struct loop_device *lo)
> {
> struct loop_info64 info64;
>
> + lockdep_assert_held(&loop_mutex);
> if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
> return -EFAULT;
> return loop_set_status(lo, &info64);
> @@ -1289,10 +1335,8 @@ static int loop_clr_fd(struct loop_device *lo)
> struct loop_info64 info64;
> int err;
>
> - if (!arg) {
> - mutex_unlock(&lo->lo_ctl_mutex);
> + if (!arg)
> return -EINVAL;
> - }
> err = loop_get_status(lo, &info64);
> if (!err)
> err = loop_info64_to_old(&info64, &info);
> @@ -1307,10 +1351,8 @@ static int loop_clr_fd(struct loop_device *lo)
> struct loop_info64 info64;
> int err;
>
> - if (!arg) {
> - mutex_unlock(&lo->lo_ctl_mutex);
> + if (!arg)
> return -EINVAL;
> - }
> err = loop_get_status(lo, &info64);
> if (!err && copy_to_user(arg, &info64, sizeof(info64)))
> err = -EFAULT;
> @@ -1320,6 +1362,7 @@ static int loop_clr_fd(struct loop_device *lo)
>
> static int loop_set_capacity(struct loop_device *lo)
> {
> + lockdep_assert_held(&loop_mutex);
> if (unlikely(lo->lo_state != Lo_bound))
> return -ENXIO;
>
> @@ -1329,6 +1372,8 @@ static int loop_set_capacity(struct loop_device *lo)
> static int loop_set_dio(struct loop_device *lo, unsigned long arg)
> {
> int error = -ENXIO;
> +
> + lockdep_assert_held(&loop_mutex);
> if (lo->lo_state != Lo_bound)
> goto out;
>
> @@ -1342,6 +1387,7 @@ static int loop_set_dio(struct loop_device *lo, unsigned long arg)
>
> static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
> {
> + lockdep_assert_held(&loop_mutex);
> if (lo->lo_state != Lo_bound)
> return -ENXIO;
>
> @@ -1364,12 +1410,10 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
> unsigned int cmd, unsigned long arg)
> {
> struct loop_device *lo = bdev->bd_disk->private_data;
> - int err;
> + int err = lock_loop_killable();
>
> - err = mutex_lock_killable_nested(&lo->lo_ctl_mutex, 1);
> if (err)
> - goto out_unlocked;
> -
> + return err;
> switch (cmd) {
> case LOOP_SET_FD:
> err = loop_set_fd(lo, mode, bdev, arg);
> @@ -1378,10 +1422,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
> err = loop_change_fd(lo, bdev, arg);
> break;
> case LOOP_CLR_FD:
> - /* loop_clr_fd would have unlocked lo_ctl_mutex on success */
> err = loop_clr_fd(lo);
> - if (!err)
> - goto out_unlocked;
> break;
> case LOOP_SET_STATUS:
> err = -EPERM;
> @@ -1391,8 +1432,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
> break;
> case LOOP_GET_STATUS:
> err = loop_get_status_old(lo, (struct loop_info __user *) arg);
> - /* loop_get_status() unlocks lo_ctl_mutex */
> - goto out_unlocked;
> + break;
> case LOOP_SET_STATUS64:
> err = -EPERM;
> if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
> @@ -1401,8 +1441,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
> break;
> case LOOP_GET_STATUS64:
> err = loop_get_status64(lo, (struct loop_info64 __user *) arg);
> - /* loop_get_status() unlocks lo_ctl_mutex */
> - goto out_unlocked;
> + break;
> case LOOP_SET_CAPACITY:
> err = -EPERM;
> if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
> @@ -1421,9 +1460,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
> default:
> err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
> }
> - mutex_unlock(&lo->lo_ctl_mutex);
> -
> -out_unlocked:
> + unlock_loop();
> return err;
> }
>
> @@ -1524,6 +1561,7 @@ struct compat_loop_info {
> struct loop_info64 info64;
> int ret;
>
> + lockdep_assert_held(&loop_mutex);
> ret = loop_info64_from_compat(arg, &info64);
> if (ret < 0)
> return ret;
> @@ -1537,10 +1575,9 @@ struct compat_loop_info {
> struct loop_info64 info64;
> int err;
>
> - if (!arg) {
> - mutex_unlock(&lo->lo_ctl_mutex);
> + lockdep_assert_held(&loop_mutex);
> + if (!arg)
> return -EINVAL;
> - }
> err = loop_get_status(lo, &info64);
> if (!err)
> err = loop_info64_to_compat(&info64, arg);
> @@ -1555,20 +1592,16 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
>
> switch(cmd) {
> case LOOP_SET_STATUS:
> - err = mutex_lock_killable(&lo->lo_ctl_mutex);
> - if (!err) {
> + err = lock_loop_killable();
> + if (!err)
> err = loop_set_status_compat(lo,
> (const struct compat_loop_info __user *)arg);
> - mutex_unlock(&lo->lo_ctl_mutex);
> - }
> break;
> case LOOP_GET_STATUS:
> - err = mutex_lock_killable(&lo->lo_ctl_mutex);
> - if (!err) {
> + err = lock_loop_killable();
> + if (!err)
> err = loop_get_status_compat(lo,
> (struct compat_loop_info __user *)arg);
> - /* loop_get_status() unlocks lo_ctl_mutex */
> - }
> break;
> case LOOP_SET_CAPACITY:
> case LOOP_CLR_FD:
> @@ -1583,6 +1616,7 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
> err = -ENOIOCTLCMD;
> break;
> }
> + unlock_loop();
> return err;
> }
> #endif
> @@ -1590,37 +1624,30 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
> static int lo_open(struct block_device *bdev, fmode_t mode)
> {
> struct loop_device *lo;
> - int err = 0;
> + int err = lock_loop_killable();
>
> - mutex_lock(&loop_index_mutex);
> + if (err)
> + return err;
> lo = bdev->bd_disk->private_data;
> - if (!lo) {
> + if (!lo)
> err = -ENXIO;
> - goto out;
> - }
> -
> - atomic_inc(&lo->lo_refcnt);
> -out:
> - mutex_unlock(&loop_index_mutex);
> + else
> + atomic_inc(&lo->lo_refcnt);
> + unlock_loop();
> return err;
> }
>
> static void __lo_release(struct loop_device *lo)
> {
> - int err;
> -
> if (atomic_dec_return(&lo->lo_refcnt))
> return;
> -
> - mutex_lock(&lo->lo_ctl_mutex);
> + lockdep_assert_held(&loop_mutex);
> if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
> /*
> * In autoclear mode, stop the loop thread
> * and remove configuration after last close.
> */
> - err = loop_clr_fd(lo);
> - if (!err)
> - return;
> + loop_clr_fd(lo);
> } else if (lo->lo_state == Lo_bound) {
> /*
> * Otherwise keep thread (if running) and config,
> @@ -1629,15 +1656,13 @@ static void __lo_release(struct loop_device *lo)
> blk_mq_freeze_queue(lo->lo_queue);
> blk_mq_unfreeze_queue(lo->lo_queue);
> }
> -
> - mutex_unlock(&lo->lo_ctl_mutex);
> }
>
> static void lo_release(struct gendisk *disk, fmode_t mode)
> {
> - mutex_lock(&loop_index_mutex);
> + lock_loop();
> __lo_release(disk->private_data);
> - mutex_unlock(&loop_index_mutex);
> + unlock_loop();
> }
>
> static const struct block_device_operations lo_fops = {
> @@ -1676,10 +1701,8 @@ static int unregister_transfer_cb(int id, void *ptr, void *data)
> struct loop_device *lo = ptr;
> struct loop_func_table *xfer = data;
>
> - mutex_lock(&lo->lo_ctl_mutex);
> if (lo->lo_encryption == xfer)
> loop_release_xfer(lo);
> - mutex_unlock(&lo->lo_ctl_mutex);
> return 0;
> }
>
> @@ -1691,8 +1714,14 @@ int loop_unregister_transfer(int number)
> if (n == 0 || n >= MAX_LO_CRYPT || (xfer = xfer_funcs[n]) == NULL)
> return -EINVAL;
>
> + /*
> + * cleanup_cryptoloop() cannot handle errors because it is called
> + * from module_exit(). Thus, don't give up upon SIGKILL here.
> + */
> + lock_loop();
> xfer_funcs[n] = NULL;
> idr_for_each(&loop_index_idr, &unregister_transfer_cb, xfer);
> + unlock_loop();
> return 0;
> }
>
> @@ -1860,7 +1889,6 @@ static int loop_add(struct loop_device **l, int i)
> if (!part_shift)
> disk->flags |= GENHD_FL_NO_PART_SCAN;
> disk->flags |= GENHD_FL_EXT_DEVT;
> - mutex_init(&lo->lo_ctl_mutex);
> atomic_set(&lo->lo_refcnt, 0);
> lo->lo_number = i;
> spin_lock_init(&lo->lo_lock);
> @@ -1936,20 +1964,19 @@ static int loop_lookup(struct loop_device **l, int i)
> static struct kobject *loop_probe(dev_t dev, int *part, void *data)
> {
> struct loop_device *lo;
> - struct kobject *kobj;
> - int err;
> + struct kobject *kobj = NULL;
> + int err = lock_loop_killable();
>
> - mutex_lock(&loop_index_mutex);
> + *part = 0;
> + if (err)
> + return NULL;
> err = loop_lookup(&lo, MINOR(dev) >> part_shift);
> if (err < 0)
> err = loop_add(&lo, MINOR(dev) >> part_shift);
> - if (err < 0)
> - kobj = NULL;
> - else
> + if (err >= 0)
> kobj = get_disk_and_module(lo->lo_disk);
> - mutex_unlock(&loop_index_mutex);
> + unlock_loop();
>
> - *part = 0;
> return kobj;
> }
>
> @@ -1957,9 +1984,11 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
> unsigned long parm)
> {
> struct loop_device *lo;
> - int ret = -ENOSYS;
> + int ret = lock_loop_killable();
>
> - mutex_lock(&loop_index_mutex);
> + if (ret)
> + return ret;
> + ret = -ENOSYS;
> switch (cmd) {
> case LOOP_CTL_ADD:
> ret = loop_lookup(&lo, parm);
> @@ -1973,21 +2002,17 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
> ret = loop_lookup(&lo, parm);
> if (ret < 0)
> break;
> - ret = mutex_lock_killable(&lo->lo_ctl_mutex);
> if (ret)
> break;
> if (lo->lo_state != Lo_unbound) {
> ret = -EBUSY;
> - mutex_unlock(&lo->lo_ctl_mutex);
> break;
> }
> if (atomic_read(&lo->lo_refcnt) > 0) {
> ret = -EBUSY;
> - mutex_unlock(&lo->lo_ctl_mutex);
> break;
> }
> lo->lo_disk->private_data = NULL;
> - mutex_unlock(&lo->lo_ctl_mutex);
> idr_remove(&loop_index_idr, lo->lo_number);
> loop_remove(lo);
> break;
> @@ -1997,7 +2022,7 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
> break;
> ret = loop_add(&lo, -1);
> }
> - mutex_unlock(&loop_index_mutex);
> + unlock_loop();
>
> return ret;
> }
> @@ -2081,10 +2106,10 @@ static int __init loop_init(void)
> THIS_MODULE, loop_probe, NULL, NULL);
>
> /* pre-create number of devices given by config or max_loop */
> - mutex_lock(&loop_index_mutex);
> + lock_loop();
> for (i = 0; i < nr; i++)
> loop_add(&lo, i);
> - mutex_unlock(&loop_index_mutex);
> + unlock_loop();
>
> printk(KERN_INFO "loop: module loaded\n");
> return 0;
> diff --git a/drivers/block/loop.h b/drivers/block/loop.h
> index 0f45416..61c6421 100644
> --- a/drivers/block/loop.h
> +++ b/drivers/block/loop.h
> @@ -54,7 +54,6 @@ struct loop_device {
>
> spinlock_t lo_lock;
> int lo_state;
> - struct mutex lo_ctl_mutex;
> struct kthread_worker worker;
> struct task_struct *worker_task;
> bool use_dio;
> --
> 1.8.3.1
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