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Commit aaa2cacf authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
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writeback: add lockdep annotation to inode_to_wb() 



With the previous three patches, all operations which acquire wb from
inode are either under one of inode->i_lock, mapping->tree_lock or
wb->list_lock or protected by unlocked_inode_to_wb transaction.  This
will be depended upon by foreign inode wb switching.

This patch adds lockdep assertion to inode_to_wb() so that usages
outside the above list locks can be caught easily.  There are three
exceptions.

* locked_inode_to_wb_and_lock_list() is holding wb->list_lock but the
  wb may not be the inode's.  Ensuring that is the function's role
  after all.  Updated to deref inode->i_wb directly.

* inode_wb_stat_unlocked_begin() is usually protected by combination
  of !I_WB_SWITCH and rcu_read_lock().  Updated to deref inode->i_wb
  directly.

* inode_congested() wants to test whether inode->i_wb is set before
  starting the transaction.  Added inode_to_wb_is_valid() which tests
  inode->i_wb directly.

v5: might_lock() removed.  It annotates that the lock is grabbed w/
    irq enabled which isn't the case and triggering lockdep warning
    spuriously.

v4: might_lock() added to unlocked_inode_to_wb_begin().

v3: inode_congested() conversion added.

v2: locked_inode_to_wb_and_lock_list() was missing in the first
    version.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 5cb8b824

fs/fs-writeback.c

+3 −2
Original line number Diff line number Diff line
@@ -285,7 +285,8 @@ locked_inode_to_wb_and_lock_list(struct inode *inode) 
		spin_lock(&wb->list_lock);

		wb_put(wb);		/* not gonna deref it anymore */



		if (likely(wb == inode_to_wb(inode)))

		/* i_wb may have changed inbetween, can't use inode_to_wb() */

		if (likely(wb == inode->i_wb))

			return wb;	/* @inode already has ref */



		spin_unlock(&wb->list_lock);
@@ -622,7 +623,7 @@ int inode_congested(struct inode *inode, int cong_bits) 
	 * Once set, ->i_wb never becomes NULL while the inode is alive.

	 * Start transaction iff ->i_wb is visible.

	 */

	if (inode && inode_to_wb(inode)) {

	if (inode && inode_to_wb_is_valid(inode)) {

		struct bdi_writeback *wb;

		bool locked, congested;

include/linux/backing-dev.h

+32 −2
Original line number Diff line number Diff line
@@ -321,14 +321,34 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp) 
	return wb;

}



/**

 * inode_to_wb_is_valid - test whether an inode has a wb associated

 * @inode: inode of interest

 *

 * Returns %true if @inode has a wb associated.  May be called without any

 * locking.

 */

static inline bool inode_to_wb_is_valid(struct inode *inode)

{

	return inode->i_wb;

}



/**

 * inode_to_wb - determine the wb of an inode

 * @inode: inode of interest

 *

 * Returns the wb @inode is currently associated with.

 * Returns the wb @inode is currently associated with.  The caller must be

 * holding either @inode->i_lock, @inode->i_mapping->tree_lock, or the

 * associated wb's list_lock.

 */

static inline struct bdi_writeback *inode_to_wb(struct inode *inode)

{

#ifdef CONFIG_LOCKDEP

	WARN_ON_ONCE(debug_locks &&

		     (!lockdep_is_held(&inode->i_lock) &&

		      !lockdep_is_held(&inode->i_mapping->tree_lock) &&

		      !lockdep_is_held(&inode->i_wb->list_lock)));

#endif

	return inode->i_wb;

}
@@ -360,7 +380,12 @@ unlocked_inode_to_wb_begin(struct inode *inode, bool *lockedp) 


	if (unlikely(*lockedp))

		spin_lock_irq(&inode->i_mapping->tree_lock);

	return inode_to_wb(inode);



	/*

	 * Protected by either !I_WB_SWITCH + rcu_read_lock() or tree_lock.

	 * inode_to_wb() will bark.  Deref directly.

	 */

	return inode->i_wb;

}



/**
@@ -459,6 +484,11 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp) 
	return &bdi->wb;

}



static inline bool inode_to_wb_is_valid(struct inode *inode)

{

	return true;

}



static inline struct bdi_writeback *inode_to_wb(struct inode *inode)

{

	return &inode_to_bdi(inode)->wb;