From 356c05d58af05d582e634b54b40050c73609617b Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Mon, 14 May 2012 13:30:03 -0400 Subject: sysfs: get rid of some lockdep false positives This patch (as1554) fixes a lockdep false-positive report. The problem arises because lockdep is unable to deal with the tree-structured locks created by the device core and sysfs. This particular problem involves a sysfs attribute method that unregisters itself, not from the device it was called for, but from a descendant device. Lockdep doesn't understand the distinction and reports a possible deadlock, even though the operation is safe. This is the sort of thing that would normally be handled by using a nested lock annotation; unfortunately it's not feasible to do that here. There's no sensible way to tell sysfs when attribute removal occurs in the context of a parent attribute method. As a workaround, the patch adds a new flag to struct attribute telling sysfs not to inform lockdep when it acquires a readlock on a sysfs_dirent instance for the attribute. The readlock is still acquired, but lockdep doesn't know about it and hence does not complain about impossible deadlock scenarios. Also added are macros for static initialization of attribute structures with the ignore_lockdep flag set. The three offending attributes in the USB subsystem are converted to use the new macros. Signed-off-by: Alan Stern Acked-by: Tejun Heo CC: Eric W. Biederman CC: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c index 566d9f9..9a56e3a 100644 --- a/drivers/usb/core/sysfs.c +++ b/drivers/usb/core/sysfs.c @@ -73,7 +73,7 @@ set_bConfigurationValue(struct device *dev, struct device_attribute *attr, return (value < 0) ? value : count; } -static DEVICE_ATTR(bConfigurationValue, S_IRUGO | S_IWUSR, +static DEVICE_ATTR_IGNORE_LOCKDEP(bConfigurationValue, S_IRUGO | S_IWUSR, show_bConfigurationValue, set_bConfigurationValue); /* String fields */ @@ -595,7 +595,7 @@ static ssize_t usb_dev_authorized_store(struct device *dev, return result < 0? result : size; } -static DEVICE_ATTR(authorized, 0644, +static DEVICE_ATTR_IGNORE_LOCKDEP(authorized, 0644, usb_dev_authorized_show, usb_dev_authorized_store); /* "Safely remove a device" */ @@ -618,7 +618,7 @@ static ssize_t usb_remove_store(struct device *dev, usb_unlock_device(udev); return rc; } -static DEVICE_ATTR(remove, 0200, NULL, usb_remove_store); +static DEVICE_ATTR_IGNORE_LOCKDEP(remove, 0200, NULL, usb_remove_store); static struct attribute *dev_attrs[] = { diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index 24fa995..e6bb9b2 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -132,6 +132,24 @@ static void sysfs_unlink_sibling(struct sysfs_dirent *sd) rb_erase(&sd->s_rb, &sd->s_parent->s_dir.children); } +#ifdef CONFIG_DEBUG_LOCK_ALLOC + +/* Test for attributes that want to ignore lockdep for read-locking */ +static bool ignore_lockdep(struct sysfs_dirent *sd) +{ + return sysfs_type(sd) == SYSFS_KOBJ_ATTR && + sd->s_attr.attr->ignore_lockdep; +} + +#else + +static inline bool ignore_lockdep(struct sysfs_dirent *sd) +{ + return true; +} + +#endif + /** * sysfs_get_active - get an active reference to sysfs_dirent * @sd: sysfs_dirent to get an active reference to @@ -155,15 +173,17 @@ struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd) return NULL; t = atomic_cmpxchg(&sd->s_active, v, v + 1); - if (likely(t == v)) { - rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_); - return sd; - } + if (likely(t == v)) + break; if (t < 0) return NULL; cpu_relax(); } + + if (likely(!ignore_lockdep(sd))) + rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_); + return sd; } /** @@ -180,7 +200,8 @@ void sysfs_put_active(struct sysfs_dirent *sd) if (unlikely(!sd)) return; - rwsem_release(&sd->dep_map, 1, _RET_IP_); + if (likely(!ignore_lockdep(sd))) + rwsem_release(&sd->dep_map, 1, _RET_IP_); v = atomic_dec_return(&sd->s_active); if (likely(v != SD_DEACTIVATED_BIAS)) return; diff --git a/include/linux/device.h b/include/linux/device.h index a8db2cf..e04f577 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -504,6 +504,9 @@ ssize_t device_store_int(struct device *dev, struct device_attribute *attr, #define DEVICE_INT_ATTR(_name, _mode, _var) \ struct dev_ext_attribute dev_attr_##_name = \ { __ATTR(_name, _mode, device_show_int, device_store_int), &(_var) } +#define DEVICE_ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store) \ + struct device_attribute dev_attr_##_name = \ + __ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store) extern int device_create_file(struct device *device, const struct device_attribute *entry); diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h index 0010009..381f06d 100644 --- a/include/linux/sysfs.h +++ b/include/linux/sysfs.h @@ -27,6 +27,7 @@ struct attribute { const char *name; umode_t mode; #ifdef CONFIG_DEBUG_LOCK_ALLOC + bool ignore_lockdep:1; struct lock_class_key *key; struct lock_class_key skey; #endif @@ -80,6 +81,17 @@ struct attribute_group { #define __ATTR_NULL { .attr = { .name = NULL } } +#ifdef CONFIG_DEBUG_LOCK_ALLOC +#define __ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store) { \ + .attr = {.name = __stringify(_name), .mode = _mode, \ + .ignore_lockdep = true }, \ + .show = _show, \ + .store = _store, \ +} +#else +#define __ATTR_IGNORE_LOCKDEP __ATTR +#endif + #define attr_name(_attr) (_attr).attr.name struct file; -- cgit v0.10.2