Commit 3ce6e1f662a91097 ("loop: reintroduce global lock for safe
loop_validate_file() traversal") had to use a mutex in order to avoid
AB-BA deadlock. But commit c895b784c699224d ("loop: don't hold lo_mutex
during __loop_clr_fd()") suggested me that we can also avoid AB-BA
deadlock without a mutex if we use dedicated state for individual
operations.
Thus, introduce Lo_binding state in order to allow loop_change_fd() and
loop_configure() to do their operations without holding lo_mutex, and
update loop_validate_file() to use a global spinlock.
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
drivers/block/loop.c | 153 +++++++++++++++++--------------------------
drivers/block/loop.h | 1 +
2 files changed, 60 insertions(+), 94 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index ba76319b5544..3dfb39d38235 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -88,46 +88,46 @@
static DEFINE_IDR(loop_index_idr);
static DEFINE_MUTEX(loop_ctl_mutex);
-static DEFINE_MUTEX(loop_validate_mutex);
+static DEFINE_SPINLOCK(loop_validate_spinlock);
-/**
- * loop_global_lock_killable() - take locks for safe loop_validate_file() test
- *
- * @lo: struct loop_device
- * @global: true if @lo is about to bind another "struct loop_device", false otherwise
- *
- * Returns 0 on success, -EINTR otherwise.
- *
- * Since loop_validate_file() traverses on other "struct loop_device" if
- * is_loop_device() is true, we need a global lock for serializing concurrent
- * loop_configure()/loop_change_fd()/__loop_clr_fd() calls.
- */
-static int loop_global_lock_killable(struct loop_device *lo, bool global)
+static bool loop_try_update_state_locked(struct loop_device *lo, const int old, const int new)
{
- int err;
+ bool ret = false;
- if (global) {
- err = mutex_lock_killable(&loop_validate_mutex);
- if (err)
- return err;
+ lockdep_assert_held(&lo->lo_mutex);
+ spin_lock(&loop_validate_spinlock);
+ if (lo->lo_state == old) {
+ lo->lo_state = new;
+ ret = true;
}
- err = mutex_lock_killable(&lo->lo_mutex);
- if (err && global)
- mutex_unlock(&loop_validate_mutex);
- return err;
+ spin_unlock(&loop_validate_spinlock);
+ return ret;
}
-/**
- * loop_global_unlock() - release locks taken by loop_global_lock_killable()
- *
- * @lo: struct loop_device
- * @global: true if @lo was about to bind another "struct loop_device", false otherwise
- */
-static void loop_global_unlock(struct loop_device *lo, bool global)
+static bool loop_try_update_state(struct loop_device *lo, const int old, const int new)
{
+ bool ret;
+
+ if (mutex_lock_killable(&lo->lo_mutex))
+ return false;
+ ret = loop_try_update_state_locked(lo, old, new);
+ mutex_unlock(&lo->lo_mutex);
+ return ret;
+}
+
+static void loop_update_state_locked(struct loop_device *lo, const int state)
+{
+ lockdep_assert_held(&lo->lo_mutex);
+ spin_lock(&loop_validate_spinlock);
+ lo->lo_state = state;
+ spin_unlock(&loop_validate_spinlock);
+}
+
+static void loop_update_state(struct loop_device *lo, const int state)
+{
+ mutex_lock(&lo->lo_mutex);
+ loop_update_state_locked(lo, state);
mutex_unlock(&lo->lo_mutex);
- if (global)
- mutex_unlock(&loop_validate_mutex);
}
static int max_part;
@@ -532,25 +532,28 @@ static int loop_validate_file(struct file *file, struct block_device *bdev)
{
struct inode *inode = file->f_mapping->host;
struct file *f = file;
+ int err = 0;
/* Avoid recursion */
+ spin_lock(&loop_validate_spinlock);
while (is_loop_device(f)) {
struct loop_device *l;
- lockdep_assert_held(&loop_validate_mutex);
- if (f->f_mapping->host->i_rdev == bdev->bd_dev)
- return -EBADF;
-
+ if (f->f_mapping->host->i_rdev == bdev->bd_dev) {
+ err = -EBADF;
+ break;
+ }
l = I_BDEV(f->f_mapping->host)->bd_disk->private_data;
- if (l->lo_state != Lo_bound)
- return -EINVAL;
- /* Order wrt setting lo->lo_backing_file in loop_configure(). */
- rmb();
+ if (l->lo_state != Lo_bound) {
+ err = -EINVAL;
+ break;
+ }
f = l->lo_backing_file;
}
- if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
- return -EINVAL;
- return 0;
+ if (!err && !S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
+ err = -EINVAL;
+ spin_unlock(&loop_validate_spinlock);
+ return err;
}
/*
@@ -568,17 +571,12 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
struct file *old_file;
int error;
bool partscan;
- bool is_loop;
if (!file)
return -EBADF;
- is_loop = is_loop_device(file);
- error = loop_global_lock_killable(lo, is_loop);
- if (error)
- goto out_putf;
error = -ENXIO;
- if (lo->lo_state != Lo_bound)
- goto out_err;
+ if (!loop_try_update_state(lo, Lo_bound, Lo_binding))
+ goto out_putf;
/* the loop device has to be read-only */
error = -EINVAL;
@@ -608,16 +606,8 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
loop_update_dio(lo);
blk_mq_unfreeze_queue(lo->lo_queue);
partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
- loop_global_unlock(lo, is_loop);
+ loop_update_state(lo, Lo_bound);
- /*
- * Flush loop_validate_file() before fput(), for l->lo_backing_file
- * might be pointing at old_file which might be the last reference.
- */
- if (!is_loop) {
- mutex_lock(&loop_validate_mutex);
- mutex_unlock(&loop_validate_mutex);
- }
/*
* We must drop file reference outside of lo_mutex as dropping
* the file ref can take open_mutex which creates circular locking
@@ -629,7 +619,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
return 0;
out_err:
- loop_global_unlock(lo, is_loop);
+ loop_update_state(lo, Lo_bound);
out_putf:
fput(file);
return error;
@@ -953,11 +943,9 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
loff_t size;
bool partscan;
unsigned short bsize;
- bool is_loop;
if (!file)
return -EBADF;
- is_loop = is_loop_device(file);
/* This is safe, since we have a reference from open(). */
__module_get(THIS_MODULE);
@@ -972,13 +960,9 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
goto out_putf;
}
- error = loop_global_lock_killable(lo, is_loop);
- if (error)
- goto out_bdev;
-
error = -EBUSY;
- if (lo->lo_state != Lo_unbound)
- goto out_unlock;
+ if (!loop_try_update_state(lo, Lo_unbound, Lo_binding))
+ goto out_bdev;
error = loop_validate_file(file, bdev);
if (error)
@@ -1053,17 +1037,13 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
size = get_loop_size(lo, file);
loop_set_size(lo, size);
- /* Order wrt reading lo_state in loop_validate_file(). */
- wmb();
-
- lo->lo_state = Lo_bound;
if (part_shift)
lo->lo_flags |= LO_FLAGS_PARTSCAN;
partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
if (partscan)
lo->lo_disk->flags &= ~GENHD_FL_NO_PART;
- loop_global_unlock(lo, is_loop);
+ loop_update_state(lo, Lo_bound);
if (partscan)
loop_reread_partitions(lo);
if (!(mode & FMODE_EXCL))
@@ -1071,7 +1051,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
return 0;
out_unlock:
- loop_global_unlock(lo, is_loop);
+ loop_update_state(lo, Lo_unbound);
out_bdev:
if (!(mode & FMODE_EXCL))
bd_abort_claiming(bdev, loop_configure);
@@ -1088,18 +1068,6 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
gfp_t gfp = lo->old_gfp_mask;
struct loop_worker *pos, *worker;
- /*
- * Flush loop_configure() and loop_change_fd(). It is acceptable for
- * loop_validate_file() to succeed, for actual clear operation has not
- * started yet.
- */
- mutex_lock(&loop_validate_mutex);
- mutex_unlock(&loop_validate_mutex);
- /*
- * loop_validate_file() now fails because l->lo_state != Lo_bound
- * became visible.
- */
-
/*
* Since this function is called upon "ioctl(LOOP_CLR_FD)" xor "close()
* after ioctl(LOOP_CLR_FD)", it is a sign of something going wrong if
@@ -1181,9 +1149,7 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
lo->lo_flags = 0;
if (!part_shift)
lo->lo_disk->flags |= GENHD_FL_NO_PART;
- mutex_lock(&lo->lo_mutex);
- lo->lo_state = Lo_unbound;
- mutex_unlock(&lo->lo_mutex);
+ loop_update_state(lo, Lo_unbound);
/*
* Need not hold lo_mutex to fput backing file. Calling fput holding
@@ -1219,7 +1185,7 @@ static int loop_clr_fd(struct loop_device *lo)
mutex_unlock(&lo->lo_mutex);
return 0;
}
- lo->lo_state = Lo_rundown;
+ loop_update_state_locked(lo, Lo_rundown);
mutex_unlock(&lo->lo_mutex);
__loop_clr_fd(lo, false);
@@ -1739,9 +1705,8 @@ static void lo_release(struct gendisk *disk, fmode_t mode)
goto out_unlock;
if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
- if (lo->lo_state != Lo_bound)
+ if (!loop_try_update_state_locked(lo, Lo_bound, Lo_rundown))
goto out_unlock;
- lo->lo_state = Lo_rundown;
mutex_unlock(&lo->lo_mutex);
/*
* In autoclear mode, stop the loop thread
@@ -1953,7 +1918,6 @@ static int loop_add(int i)
lo = kzalloc(sizeof(*lo), GFP_KERNEL);
if (!lo)
goto out;
- lo->lo_state = Lo_unbound;
err = mutex_lock_killable(&loop_ctl_mutex);
if (err)
@@ -2024,6 +1988,7 @@ static int loop_add(int i)
disk->flags |= GENHD_FL_NO_PART;
atomic_set(&lo->lo_refcnt, 0);
mutex_init(&lo->lo_mutex);
+ loop_update_state(lo, Lo_unbound);
lo->lo_number = i;
spin_lock_init(&lo->lo_lock);
spin_lock_init(&lo->lo_work_lock);
@@ -2119,7 +2084,7 @@ static int loop_control_remove(int idx)
goto mark_visible;
}
/* Mark this loop device no longer open()-able. */
- lo->lo_state = Lo_deleting;
+ loop_update_state_locked(lo, Lo_deleting);
mutex_unlock(&lo->lo_mutex);
loop_remove(lo);
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 082d4b6bfc6a..56b9392737b2 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -19,6 +19,7 @@
/* Possible states of device */
enum {
Lo_unbound,
+ Lo_binding,
Lo_bound,
Lo_rundown,
Lo_deleting,
--
2.18.4
