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Commit 2d1d4c1e authored by Omar Sandoval's avatar Omar Sandoval Committed by Jens Axboe
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loop: don't call into filesystem while holding lo_ctl_mutex 



We hit an issue where a loop device on NFS was stuck in
loop_get_status() doing vfs_getattr() after the NFS server died, which
caused a pile-up of uninterruptible processes waiting on lo_ctl_mutex.
There's no reason to hold this lock while we wait on the filesystem;
let's drop it so that other processes can do their thing. We need to
grab a reference on lo_backing_file while we use it, and we can get rid
of the check on lo_device, which has been unnecessary since commit
a34c0ae9ebd6 ("[PATCH] loop: remove the bio remapping capability") in
the linux-history tree.

Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent bc56e2ca

drivers/block/loop.c

+24 −14
Original line number Diff line number Diff line
@@ -1167,21 +1167,17 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) 
static int

loop_get_status(struct loop_device *lo, struct loop_info64 *info)

{

	struct file *file = lo->lo_backing_file;

	struct file *file;

	struct kstat stat;

	int error;

	int ret;



	if (lo->lo_state != Lo_bound)

	if (lo->lo_state != Lo_bound) {

		mutex_unlock(&lo->lo_ctl_mutex);

		return -ENXIO;

	error = vfs_getattr(&file->f_path, &stat,

			    STATX_INO, AT_STATX_SYNC_AS_STAT);

	if (error)

		return error;

	}



	memset(info, 0, sizeof(*info));

	info->lo_number = lo->lo_number;

	info->lo_device = huge_encode_dev(stat.dev);

	info->lo_inode = stat.ino;

	info->lo_rdevice = huge_encode_dev(lo->lo_device ? stat.rdev : stat.dev);

	info->lo_offset = lo->lo_offset;

	info->lo_sizelimit = lo->lo_sizelimit;

	info->lo_flags = lo->lo_flags;
@@ -1194,7 +1190,19 @@ loop_get_status(struct loop_device *lo, struct loop_info64 *info) 
		memcpy(info->lo_encrypt_key, lo->lo_encrypt_key,

		       lo->lo_encrypt_key_size);

	}

	return 0;



	/* 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);

	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);

	return ret;

}



static void
@@ -1374,7 +1382,8 @@ 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);

		break;

		/* loop_get_status() unlocks lo_ctl_mutex */

		goto out_unlocked;

	case LOOP_SET_STATUS64:

		err = -EPERM;

		if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
@@ -1383,7 +1392,8 @@ 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);

		break;

		/* loop_get_status() unlocks lo_ctl_mutex */

		goto out_unlocked;

	case LOOP_SET_CAPACITY:

		err = -EPERM;

		if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
@@ -1544,7 +1554,7 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, 
		mutex_lock(&lo->lo_ctl_mutex);

		err = loop_get_status_compat(

			lo, (struct compat_loop_info __user *) arg);

		mutex_unlock(&lo->lo_ctl_mutex);

		/* loop_get_status() unlocks lo_ctl_mutex */

		break;

	case LOOP_SET_CAPACITY:

	case LOOP_CLR_FD: