fs: kill i_alloc_sem
i_alloc_sem is a rather special rw_semaphore. It's the last one that may be released by a non-owner, and it's write side is always mirrored by real exclusion. It's intended use it to wait for all pending direct I/O requests to finish before starting a truncate. Replace it with a hand-grown construct: - exclusion for truncates is already guaranteed by i_mutex, so it can simply fall way - the reader side is replaced by an i_dio_count member in struct inode that counts the number of pending direct I/O requests. Truncate can't proceed as long as it's non-zero - when i_dio_count reaches non-zero we wake up a pending truncate using wake_up_bit on a new bit in i_flags - new references to i_dio_count can't appear while we are waiting for it to read zero because the direct I/O count always needs i_mutex (or an equivalent like XFS's i_iolock) for starting a new operation. This scheme is much simpler, and saves the space of a spinlock_t and a struct list_head in struct inode (typically 160 bits on a non-debug 64-bit system). Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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f9b5570d7f
Коммит
bd5fe6c5eb
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@ -233,16 +233,13 @@ int notify_change(struct dentry * dentry, struct iattr * attr)
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return error;
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if (ia_valid & ATTR_SIZE)
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down_write(&dentry->d_inode->i_alloc_sem);
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inode_dio_wait(inode);
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if (inode->i_op->setattr)
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error = inode->i_op->setattr(dentry, attr);
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else
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error = simple_setattr(dentry, attr);
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if (ia_valid & ATTR_SIZE)
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up_write(&dentry->d_inode->i_alloc_sem);
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if (!error)
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fsnotify_change(dentry, ia_valid);
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@ -135,6 +135,50 @@ struct dio {
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struct page *pages[DIO_PAGES]; /* page buffer */
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};
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static void __inode_dio_wait(struct inode *inode)
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{
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wait_queue_head_t *wq = bit_waitqueue(&inode->i_state, __I_DIO_WAKEUP);
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DEFINE_WAIT_BIT(q, &inode->i_state, __I_DIO_WAKEUP);
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do {
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prepare_to_wait(wq, &q.wait, TASK_UNINTERRUPTIBLE);
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if (atomic_read(&inode->i_dio_count))
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schedule();
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} while (atomic_read(&inode->i_dio_count));
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finish_wait(wq, &q.wait);
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}
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/**
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* inode_dio_wait - wait for outstanding DIO requests to finish
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* @inode: inode to wait for
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*
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* Waits for all pending direct I/O requests to finish so that we can
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* proceed with a truncate or equivalent operation.
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*
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* Must be called under a lock that serializes taking new references
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* to i_dio_count, usually by inode->i_mutex.
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*/
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void inode_dio_wait(struct inode *inode)
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{
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if (atomic_read(&inode->i_dio_count))
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__inode_dio_wait(inode);
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}
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EXPORT_SYMBOL_GPL(inode_dio_wait);
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/*
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* inode_dio_done - signal finish of a direct I/O requests
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* @inode: inode the direct I/O happens on
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*
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* This is called once we've finished processing a direct I/O request,
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* and is used to wake up callers waiting for direct I/O to be quiesced.
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*/
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void inode_dio_done(struct inode *inode)
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{
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if (atomic_dec_and_test(&inode->i_dio_count))
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wake_up_bit(&inode->i_state, __I_DIO_WAKEUP);
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}
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EXPORT_SYMBOL_GPL(inode_dio_done);
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/*
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* How many pages are in the queue?
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*/
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@ -254,9 +298,7 @@ static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is
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}
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if (dio->flags & DIO_LOCKING)
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/* lockdep: non-owner release */
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up_read_non_owner(&dio->inode->i_alloc_sem);
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inode_dio_done(dio->inode);
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return ret;
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}
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@ -980,9 +1022,6 @@ out:
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return ret;
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}
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/*
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* Releases both i_mutex and i_alloc_sem
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*/
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static ssize_t
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direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
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const struct iovec *iov, loff_t offset, unsigned long nr_segs,
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@ -1146,15 +1185,14 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
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* For writes this function is called under i_mutex and returns with
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* i_mutex held, for reads, i_mutex is not held on entry, but it is
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* taken and dropped again before returning.
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* For reads and writes i_alloc_sem is taken in shared mode and released
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* on I/O completion (which may happen asynchronously after returning to
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* the caller).
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* The i_dio_count counter keeps track of the number of outstanding
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* direct I/O requests, and truncate waits for it to reach zero.
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* New references to i_dio_count must only be grabbed with i_mutex
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* held.
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*
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* - if the flags value does NOT contain DIO_LOCKING we don't use any
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* internal locking but rather rely on the filesystem to synchronize
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* direct I/O reads/writes versus each other and truncate.
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* For reads and writes both i_mutex and i_alloc_sem are not held on
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* entry and are never taken.
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*/
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ssize_t
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__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
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@ -1234,10 +1272,9 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
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}
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/*
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* Will be released at I/O completion, possibly in a
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* different thread.
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* Will be decremented at I/O completion time.
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*/
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down_read_non_owner(&inode->i_alloc_sem);
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atomic_inc(&inode->i_dio_count);
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}
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/*
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@ -168,8 +168,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
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mutex_init(&inode->i_mutex);
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lockdep_set_class(&inode->i_mutex, &sb->s_type->i_mutex_key);
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init_rwsem(&inode->i_alloc_sem);
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lockdep_set_class(&inode->i_alloc_sem, &sb->s_type->i_alloc_sem_key);
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atomic_set(&inode->i_dio_count, 0);
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mapping->a_ops = &empty_aops;
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mapping->host = inode;
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@ -1832,9 +1832,8 @@ static ssize_t ntfs_file_buffered_write(struct kiocb *iocb,
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* fails again.
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*/
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if (unlikely(NInoTruncateFailed(ni))) {
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down_write(&vi->i_alloc_sem);
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inode_dio_wait(vi);
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err = ntfs_truncate(vi);
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up_write(&vi->i_alloc_sem);
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if (err || NInoTruncateFailed(ni)) {
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if (!err)
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err = -EIO;
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@ -2357,12 +2357,7 @@ static const char *es = " Leaving inconsistent metadata. Unmount and run "
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*
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* Returns 0 on success or -errno on error.
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*
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* Called with ->i_mutex held. In all but one case ->i_alloc_sem is held for
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* writing. The only case in the kernel where ->i_alloc_sem is not held is
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* mm/filemap.c::generic_file_buffered_write() where vmtruncate() is called
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* with the current i_size as the offset. The analogous place in NTFS is in
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* fs/ntfs/file.c::ntfs_file_buffered_write() where we call vmtruncate() again
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* without holding ->i_alloc_sem.
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* Called with ->i_mutex held.
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*/
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int ntfs_truncate(struct inode *vi)
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{
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@ -2887,8 +2882,7 @@ void ntfs_truncate_vfs(struct inode *vi) {
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* We also abort all changes of user, group, and mode as we do not implement
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* the NTFS ACLs yet.
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*
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* Called with ->i_mutex held. For the ATTR_SIZE (i.e. ->truncate) case, also
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* called with ->i_alloc_sem held for writing.
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* Called with ->i_mutex held.
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*/
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int ntfs_setattr(struct dentry *dentry, struct iattr *attr)
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{
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@ -551,9 +551,8 @@ bail:
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/*
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* ocfs2_dio_end_io is called by the dio core when a dio is finished. We're
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* particularly interested in the aio/dio case. Like the core uses
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* i_alloc_sem, we use the rw_lock DLM lock to protect io on one node from
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* truncation on another.
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* particularly interested in the aio/dio case. We use the rw_lock DLM lock
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* to protect io on one node from truncation on another.
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*/
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static void ocfs2_dio_end_io(struct kiocb *iocb,
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loff_t offset,
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@ -569,7 +568,7 @@ static void ocfs2_dio_end_io(struct kiocb *iocb,
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BUG_ON(!ocfs2_iocb_is_rw_locked(iocb));
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if (ocfs2_iocb_is_sem_locked(iocb)) {
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up_read(&inode->i_alloc_sem);
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inode_dio_done(inode);
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ocfs2_iocb_clear_sem_locked(iocb);
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}
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@ -2236,9 +2236,9 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
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ocfs2_iocb_clear_sem_locked(iocb);
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relock:
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/* to match setattr's i_mutex -> i_alloc_sem -> rw_lock ordering */
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/* to match setattr's i_mutex -> rw_lock ordering */
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if (direct_io) {
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down_read(&inode->i_alloc_sem);
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atomic_inc(&inode->i_dio_count);
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have_alloc_sem = 1;
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/* communicate with ocfs2_dio_end_io */
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ocfs2_iocb_set_sem_locked(iocb);
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@ -2290,7 +2290,7 @@ relock:
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*/
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if (direct_io && !can_do_direct) {
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ocfs2_rw_unlock(inode, rw_level);
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up_read(&inode->i_alloc_sem);
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inode_dio_done(inode);
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have_alloc_sem = 0;
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rw_level = -1;
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@ -2361,8 +2361,7 @@ out_dio:
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/*
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* deep in g_f_a_w_n()->ocfs2_direct_IO we pass in a ocfs2_dio_end_io
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* function pointer which is called when o_direct io completes so that
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* it can unlock our rw lock. (it's the clustered equivalent of
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* i_alloc_sem; protects truncate from racing with pending ios).
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* it can unlock our rw lock.
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* Unfortunately there are error cases which call end_io and others
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* that don't. so we don't have to unlock the rw_lock if either an
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* async dio is going to do it in the future or an end_io after an
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@ -2379,7 +2378,7 @@ out:
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out_sems:
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if (have_alloc_sem) {
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up_read(&inode->i_alloc_sem);
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inode_dio_done(inode);
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ocfs2_iocb_clear_sem_locked(iocb);
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}
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@ -2531,8 +2530,8 @@ static ssize_t ocfs2_file_aio_read(struct kiocb *iocb,
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* need locks to protect pending reads from racing with truncate.
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*/
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if (filp->f_flags & O_DIRECT) {
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down_read(&inode->i_alloc_sem);
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have_alloc_sem = 1;
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atomic_inc(&inode->i_dio_count);
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ocfs2_iocb_set_sem_locked(iocb);
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ret = ocfs2_rw_lock(inode, 0);
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bail:
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if (have_alloc_sem) {
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up_read(&inode->i_alloc_sem);
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inode_dio_done(inode);
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ocfs2_iocb_clear_sem_locked(iocb);
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}
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if (rw_level != -1)
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@ -555,11 +555,10 @@ reiserfs_xattr_set_handle(struct reiserfs_transaction_handle *th,
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reiserfs_write_unlock(inode->i_sb);
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mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_XATTR);
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down_write(&dentry->d_inode->i_alloc_sem);
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inode_dio_wait(dentry->d_inode);
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reiserfs_write_lock(inode->i_sb);
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err = reiserfs_setattr(dentry, &newattrs);
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up_write(&dentry->d_inode->i_alloc_sem);
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mutex_unlock(&dentry->d_inode->i_mutex);
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} else
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update_ctime(inode);
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@ -779,7 +779,7 @@ struct inode {
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struct timespec i_ctime;
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blkcnt_t i_blocks;
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unsigned short i_bytes;
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struct rw_semaphore i_alloc_sem;
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atomic_t i_dio_count;
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const struct file_operations *i_fop; /* former ->i_op->default_file_ops */
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struct file_lock *i_flock;
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struct address_space *i_mapping;
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@ -1705,6 +1705,10 @@ struct super_operations {
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* set during data writeback, and cleared with a wakeup
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* on the bit address once it is done.
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*
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* I_REFERENCED Marks the inode as recently references on the LRU list.
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*
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* I_DIO_WAKEUP Never set. Only used as a key for wait_on_bit().
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*
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* Q: What is the difference between I_WILL_FREE and I_FREEING?
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*/
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#define I_DIRTY_SYNC (1 << 0)
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@ -1718,6 +1722,8 @@ struct super_operations {
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#define __I_SYNC 7
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#define I_SYNC (1 << __I_SYNC)
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#define I_REFERENCED (1 << 8)
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#define __I_DIO_WAKEUP 9
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#define I_DIO_WAKEUP (1 << I_DIO_WAKEUP)
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#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)
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@ -1828,7 +1834,6 @@ struct file_system_type {
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struct lock_class_key i_lock_key;
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struct lock_class_key i_mutex_key;
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struct lock_class_key i_mutex_dir_key;
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struct lock_class_key i_alloc_sem_key;
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};
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extern struct dentry *mount_ns(struct file_system_type *fs_type, int flags,
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@ -2404,6 +2409,8 @@ enum {
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};
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void dio_end_io(struct bio *bio, int error);
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void inode_dio_wait(struct inode *inode);
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void inode_dio_done(struct inode *inode);
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ssize_t __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
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struct block_device *bdev, const struct iovec *iov, loff_t offset,
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@ -78,9 +78,6 @@
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* ->i_mutex (generic_file_buffered_write)
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* ->mmap_sem (fault_in_pages_readable->do_page_fault)
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*
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* ->i_mutex
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* ->i_alloc_sem (various)
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*
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* inode_wb_list_lock
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* sb_lock (fs/fs-writeback.c)
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* ->mapping->tree_lock (__sync_single_inode)
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@ -218,7 +218,7 @@ static long madvise_remove(struct vm_area_struct *vma,
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endoff = (loff_t)(end - vma->vm_start - 1)
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+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
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/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
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/* vmtruncate_range needs to take i_mutex */
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up_read(¤t->mm->mmap_sem);
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error = vmtruncate_range(mapping->host, offset, endoff);
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down_read(¤t->mm->mmap_sem);
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@ -21,7 +21,6 @@
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* Lock ordering in mm:
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*
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* inode->i_mutex (while writing or truncating, not reading or faulting)
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* inode->i_alloc_sem (vmtruncate_range)
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* mm->mmap_sem
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* page->flags PG_locked (lock_page)
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* mapping->i_mmap_mutex
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@ -622,12 +622,11 @@ int vmtruncate_range(struct inode *inode, loff_t offset, loff_t end)
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return -ENOSYS;
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mutex_lock(&inode->i_mutex);
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down_write(&inode->i_alloc_sem);
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inode_dio_wait(inode);
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unmap_mapping_range(mapping, offset, (end - offset), 1);
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inode->i_op->truncate_range(inode, offset, end);
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/* unmap again to remove racily COWed private pages */
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unmap_mapping_range(mapping, offset, (end - offset), 1);
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up_write(&inode->i_alloc_sem);
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mutex_unlock(&inode->i_mutex);
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return 0;
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