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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: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Omar Sandoval 2018-03-26 21:39:11 -07:00 committed by Jens Axboe
parent bc56e2cafa
commit 2d1d4c1e59
1 changed files with 24 additions and 14 deletions
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38
drivers/block/loop.c
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@ -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: