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netfs: Implement unbuffered/DIO vs buffered I/O locking

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Borrow NFS's direct-vs-buffered I/O locking into netfslib.  Similar code is
also used in ceph.

Modify it to have the correct checker annotations for i_rwsem lock
acquisition/release and to return -ERESTARTSYS if waits are interrupted.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
This commit is contained in:
David Howells 2023-10-11 15:34:07 +01:00
parent c1ec4d7c2e
commit 46ed60dcd4
3 changed files with 227 additions and 0 deletions
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1
fs/netfs/Makefile
View File

@ -4,6 +4,7 @@ netfs-y := \
buffered_read.o \
io.o \
iterator.o \
locking.o \
main.o \
misc.o \
objects.o

216
fs/netfs/locking.c Normal file
View File

@ -0,0 +1,216 @@
// SPDX-License-Identifier: GPL-2.0
/*
* I/O and data path helper functionality.
*
* Borrowed from NFS Copyright (c) 2016 Trond Myklebust
*/
#include <linux/kernel.h>
#include <linux/netfs.h>
#include "internal.h"
/*
* inode_dio_wait_interruptible - wait for outstanding DIO requests to finish
* @inode: inode to wait for
*
* Waits for all pending direct I/O requests to finish so that we can
* proceed with a truncate or equivalent operation.
*
* Must be called under a lock that serializes taking new references
* to i_dio_count, usually by inode->i_mutex.
*/
static int inode_dio_wait_interruptible(struct inode *inode)
{
if (!atomic_read(&inode->i_dio_count))
return 0;
wait_queue_head_t *wq = bit_waitqueue(&inode->i_state, __I_DIO_WAKEUP);
DEFINE_WAIT_BIT(q, &inode->i_state, __I_DIO_WAKEUP);
for (;;) {
prepare_to_wait(wq, &q.wq_entry, TASK_INTERRUPTIBLE);
if (!atomic_read(&inode->i_dio_count))
break;
if (signal_pending(current))
break;
schedule();
}
finish_wait(wq, &q.wq_entry);
return atomic_read(&inode->i_dio_count) ? -ERESTARTSYS : 0;
}
/* Call with exclusively locked inode->i_rwsem */
static int netfs_block_o_direct(struct netfs_inode *ictx)
{
if (!test_bit(NETFS_ICTX_ODIRECT, &ictx->flags))
return 0;
clear_bit(NETFS_ICTX_ODIRECT, &ictx->flags);
return inode_dio_wait_interruptible(&ictx->inode);
}
/**
* netfs_start_io_read - declare the file is being used for buffered reads
* @inode: file inode
*
* Declare that a buffered read operation is about to start, and ensure
* that we block all direct I/O.
* On exit, the function ensures that the NETFS_ICTX_ODIRECT flag is unset,
* and holds a shared lock on inode->i_rwsem to ensure that the flag
* cannot be changed.
* In practice, this means that buffered read operations are allowed to
* execute in parallel, thanks to the shared lock, whereas direct I/O
* operations need to wait to grab an exclusive lock in order to set
* NETFS_ICTX_ODIRECT.
* Note that buffered writes and truncates both take a write lock on
* inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
*/
int netfs_start_io_read(struct inode *inode)
__acquires(inode->i_rwsem)
{
struct netfs_inode *ictx = netfs_inode(inode);
/* Be an optimist! */
if (down_read_interruptible(&inode->i_rwsem) < 0)
return -ERESTARTSYS;
if (test_bit(NETFS_ICTX_ODIRECT, &ictx->flags) == 0)
return 0;
up_read(&inode->i_rwsem);
/* Slow path.... */
if (down_write_killable(&inode->i_rwsem) < 0)
return -ERESTARTSYS;
if (netfs_block_o_direct(ictx) < 0) {
up_write(&inode->i_rwsem);
return -ERESTARTSYS;
}
downgrade_write(&inode->i_rwsem);
return 0;
}
EXPORT_SYMBOL(netfs_start_io_read);
/**
* netfs_end_io_read - declare that the buffered read operation is done
* @inode: file inode
*
* Declare that a buffered read operation is done, and release the shared
* lock on inode->i_rwsem.
*/
void netfs_end_io_read(struct inode *inode)
__releases(inode->i_rwsem)
{
up_read(&inode->i_rwsem);
}
EXPORT_SYMBOL(netfs_end_io_read);
/**
* netfs_start_io_write - declare the file is being used for buffered writes
* @inode: file inode
*
* Declare that a buffered read operation is about to start, and ensure
* that we block all direct I/O.
*/
int netfs_start_io_write(struct inode *inode)
__acquires(inode->i_rwsem)
{
struct netfs_inode *ictx = netfs_inode(inode);
if (down_write_killable(&inode->i_rwsem) < 0)
return -ERESTARTSYS;
if (netfs_block_o_direct(ictx) < 0) {
up_write(&inode->i_rwsem);
return -ERESTARTSYS;
}
return 0;
}
EXPORT_SYMBOL(netfs_start_io_write);
/**
* netfs_end_io_write - declare that the buffered write operation is done
* @inode: file inode
*
* Declare that a buffered write operation is done, and release the
* lock on inode->i_rwsem.
*/
void netfs_end_io_write(struct inode *inode)
__releases(inode->i_rwsem)
{
up_write(&inode->i_rwsem);
}
EXPORT_SYMBOL(netfs_end_io_write);
/* Call with exclusively locked inode->i_rwsem */
static int netfs_block_buffered(struct inode *inode)
{
struct netfs_inode *ictx = netfs_inode(inode);
int ret;
if (!test_bit(NETFS_ICTX_ODIRECT, &ictx->flags)) {
set_bit(NETFS_ICTX_ODIRECT, &ictx->flags);
if (inode->i_mapping->nrpages != 0) {
unmap_mapping_range(inode->i_mapping, 0, 0, 0);
ret = filemap_fdatawait(inode->i_mapping);
if (ret < 0) {
clear_bit(NETFS_ICTX_ODIRECT, &ictx->flags);
return ret;
}
}
}
return 0;
}
/**
* netfs_start_io_direct - declare the file is being used for direct i/o
* @inode: file inode
*
* Declare that a direct I/O operation is about to start, and ensure
* that we block all buffered I/O.
* On exit, the function ensures that the NETFS_ICTX_ODIRECT flag is set,
* and holds a shared lock on inode->i_rwsem to ensure that the flag
* cannot be changed.
* In practice, this means that direct I/O operations are allowed to
* execute in parallel, thanks to the shared lock, whereas buffered I/O
* operations need to wait to grab an exclusive lock in order to clear
* NETFS_ICTX_ODIRECT.
* Note that buffered writes and truncates both take a write lock on
* inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
*/
int netfs_start_io_direct(struct inode *inode)
__acquires(inode->i_rwsem)
{
struct netfs_inode *ictx = netfs_inode(inode);
int ret;
/* Be an optimist! */
if (down_read_interruptible(&inode->i_rwsem) < 0)
return -ERESTARTSYS;
if (test_bit(NETFS_ICTX_ODIRECT, &ictx->flags) != 0)
return 0;
up_read(&inode->i_rwsem);
/* Slow path.... */
if (down_write_killable(&inode->i_rwsem) < 0)
return -ERESTARTSYS;
ret = netfs_block_buffered(inode);
if (ret < 0) {
up_write(&inode->i_rwsem);
return ret;
}
downgrade_write(&inode->i_rwsem);
return 0;
}
EXPORT_SYMBOL(netfs_start_io_direct);
/**
* netfs_end_io_direct - declare that the direct i/o operation is done
* @inode: file inode
*
* Declare that a direct I/O operation is done, and release the shared
* lock on inode->i_rwsem.
*/
void netfs_end_io_direct(struct inode *inode)
__releases(inode->i_rwsem)
{
up_read(&inode->i_rwsem);
}
EXPORT_SYMBOL(netfs_end_io_direct);

10
include/linux/netfs.h
View File

@ -129,6 +129,8 @@ struct netfs_inode {
struct fscache_cookie *cache;
#endif
loff_t remote_i_size; /* Size of the remote file */
unsigned long flags;
#define NETFS_ICTX_ODIRECT 0 /* The file has DIO in progress */
};
/*
@ -310,6 +312,13 @@ ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len,
struct iov_iter *new,
iov_iter_extraction_t extraction_flags);
int netfs_start_io_read(struct inode *inode);
void netfs_end_io_read(struct inode *inode);
int netfs_start_io_write(struct inode *inode);
void netfs_end_io_write(struct inode *inode);
int netfs_start_io_direct(struct inode *inode);
void netfs_end_io_direct(struct inode *inode);
/**
* netfs_inode - Get the netfs inode context from the inode
* @inode: The inode to query
@ -335,6 +344,7 @@ static inline void netfs_inode_init(struct netfs_inode *ctx,
{
ctx->ops = ops;
ctx->remote_i_size = i_size_read(&ctx->inode);
ctx->flags = 0;
#if IS_ENABLED(CONFIG_FSCACHE)
ctx->cache = NULL;
#endif