diff options
author | Johannes Berg <johannes.berg@intel.com> | 2023-11-24 19:25:26 +0300 |
---|---|---|
committer | Johannes Berg <johannes.berg@intel.com> | 2023-11-27 13:24:55 +0300 |
commit | 8c88a474357ead632b07c70bf7f119ace8c3b39e (patch) | |
tree | 31c18cdb506b19cef567f05306f958c3d65c9dfa /fs/debugfs/file.c | |
parent | f4acfcd4deb158b96595250cc332901b282d15b0 (diff) | |
download | linux-8c88a474357ead632b07c70bf7f119ace8c3b39e.tar.xz |
debugfs: add API to allow debugfs operations cancellation
In some cases there might be longer-running hardware accesses
in debugfs files, or attempts to acquire locks, and we want
to still be able to quickly remove the files.
Introduce a cancellations API to use inside the debugfs handler
functions to be able to cancel such operations on a per-file
basis.
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Diffstat (limited to 'fs/debugfs/file.c')
-rw-r--r-- | fs/debugfs/file.c | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c index 3eff92450fd5..5568cdea3490 100644 --- a/fs/debugfs/file.c +++ b/fs/debugfs/file.c @@ -114,6 +114,8 @@ int debugfs_file_get(struct dentry *dentry) lockdep_init_map(&fsd->lockdep_map, fsd->lock_name ?: "debugfs", &fsd->key, 0); #endif + INIT_LIST_HEAD(&fsd->cancellations); + mutex_init(&fsd->cancellations_mtx); } /* @@ -156,6 +158,86 @@ void debugfs_file_put(struct dentry *dentry) } EXPORT_SYMBOL_GPL(debugfs_file_put); +/** + * debugfs_enter_cancellation - enter a debugfs cancellation + * @file: the file being accessed + * @cancellation: the cancellation object, the cancel callback + * inside of it must be initialized + * + * When a debugfs file is removed it needs to wait for all active + * operations to complete. However, the operation itself may need + * to wait for hardware or completion of some asynchronous process + * or similar. As such, it may need to be cancelled to avoid long + * waits or even deadlocks. + * + * This function can be used inside a debugfs handler that may + * need to be cancelled. As soon as this function is called, the + * cancellation's 'cancel' callback may be called, at which point + * the caller should proceed to call debugfs_leave_cancellation() + * and leave the debugfs handler function as soon as possible. + * Note that the 'cancel' callback is only ever called in the + * context of some kind of debugfs_remove(). + * + * This function must be paired with debugfs_leave_cancellation(). + */ +void debugfs_enter_cancellation(struct file *file, + struct debugfs_cancellation *cancellation) +{ + struct debugfs_fsdata *fsd; + struct dentry *dentry = F_DENTRY(file); + + INIT_LIST_HEAD(&cancellation->list); + + if (WARN_ON(!d_is_reg(dentry))) + return; + + if (WARN_ON(!cancellation->cancel)) + return; + + fsd = READ_ONCE(dentry->d_fsdata); + if (WARN_ON(!fsd || + ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))) + return; + + mutex_lock(&fsd->cancellations_mtx); + list_add(&cancellation->list, &fsd->cancellations); + mutex_unlock(&fsd->cancellations_mtx); + + /* if we're already removing wake it up to cancel */ + if (d_unlinked(dentry)) + complete(&fsd->active_users_drained); +} +EXPORT_SYMBOL_GPL(debugfs_enter_cancellation); + +/** + * debugfs_leave_cancellation - leave cancellation section + * @file: the file being accessed + * @cancellation: the cancellation previously registered with + * debugfs_enter_cancellation() + * + * See the documentation of debugfs_enter_cancellation(). + */ +void debugfs_leave_cancellation(struct file *file, + struct debugfs_cancellation *cancellation) +{ + struct debugfs_fsdata *fsd; + struct dentry *dentry = F_DENTRY(file); + + if (WARN_ON(!d_is_reg(dentry))) + return; + + fsd = READ_ONCE(dentry->d_fsdata); + if (WARN_ON(!fsd || + ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))) + return; + + mutex_lock(&fsd->cancellations_mtx); + if (!list_empty(&cancellation->list)) + list_del(&cancellation->list); + mutex_unlock(&fsd->cancellations_mtx); +} +EXPORT_SYMBOL_GPL(debugfs_leave_cancellation); + /* * Only permit access to world-readable files when the kernel is locked down. * We also need to exclude any file that has ways to write or alter it as root |