Improve the loop driver - #1164
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The purpose of loop_validate_file() is to prevent that the file descriptor of an already bound loop device is changed into a file descriptor associated with a file that depends on the loop device. This must be prevented because otherwise infinite I/O loops could be triggered and filesystems involved in this loop would become impossible to unmount. Fix loop_validate_file() by comparing gendisk pointers instead of dev_t values. Cc: Theodore Ts'o <tytso@mit.edu> Cc: stable@vger.kernel.org Fixes: d2ac838 ("loop: add recursion validation to LOOP_CHANGE_FD") Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Checking inode attributes after a loop that modifies the file pointer the inode has been derived from confuses some static analyzers. Hence swap the loop and the inode attribute check. Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Let the compiler verify __must_hold(), __guarded_by() etc. Suppress the
warnings reported for loop_global_{,un}_lock*() by adding a
__context_unsafe() annotation. Both __context_unsafe() annotations will be
removed by a later patch.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Prepare for nesting lo_mutex in loop_validate_file(). Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Annotate all functions that are called with lo_mutex held with __must_hold(&lo->lo_mutex). Add a 'lo' argument to loop_validate_file() such that a __must_hold(&lo->lo_mutex) annotation can be added to this function too. Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Protect all lo_backing_file accesses from the control path with lo->lo_mutex. Use READ_ONCE() to read lo_backing_file from the data path. Serialization of I/O path lo_backing_file reads and control path lo_backing_file changes happens by freezing the request queue. Remove lo_lock because it is no longer used. Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Fix race conditions in loop_validate_file() by adding reference counting to the file chain traversal. Ensure the file reference is kept alive during all dereferences by calling get_file() before the loop and deferring fput() until after we have locked the target device's lo_mutex and confirmed it is in the Lo_bound state. Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Now that all lo_state and lo_backing_file accesses from the control path are serialized by lo_mutex, it is no longer necessary to use memory barriers to order the lo_state and lo_backing_file accesses. Hence, remove these memory barriers. While several lockless accesses of these two member variables remain in the I/O path, these are serialized with backing file changes by freezing the request queue. See also loop_change_fd(). Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Prepare for adding a second call of __loop_change_fd(). Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Prepare for adding a second __loop_configure() call. Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Keep the behavior in loop_global_lock_killable() for the global == true case. Expand loop_global_lock_killable(lo, false) calls into a mutex_lock_killable() and a mutex_unlock() call. Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Prepare for annotating the rootcg_cmd_list member with __guarded_by(). Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Document which synchronization object protects which variable. Suppress complaints about accesses without locking in initialization and cleanup functions with context_unsafe() and __assume_ctx_lock(). Signed-off-by: Bart Van Assche <bvanassche@acm.org>
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Pull request for series with
subject: Improve the loop driver
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1149306