linux/fs/netfs/buffered_read.c
Xiubo Li fac47b43c7 netfs: do not unlock and put the folio twice
check_write_begin() will unlock and put the folio when return
non-zero.  So we should avoid unlocking and putting it twice in
netfs layer.

Change the way ->check_write_begin() works in the following two ways:

 (1) Pass it a pointer to the folio pointer, allowing it to unlock and put
     the folio prior to doing the stuff it wants to do, provided it clears
     the folio pointer.

 (2) Change the return values such that 0 with folio pointer set means
     continue, 0 with folio pointer cleared means re-get and all error
     codes indicating an error (no special treatment for -EAGAIN).

[ bagasdotme: use Sphinx code text syntax for *foliop pointer ]

Cc: stable@vger.kernel.org
Link: https://tracker.ceph.com/issues/56423
Link: https://lore.kernel.org/r/cf169f43-8ee7-8697-25da-0204d1b4343e@redhat.com
Co-developed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2022-07-14 10:10:12 +02:00

428 lines
13 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/* Network filesystem high-level buffered read support.
*
* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#include <linux/export.h>
#include <linux/task_io_accounting_ops.h>
#include "internal.h"
/*
* Unlock the folios in a read operation. We need to set PG_fscache on any
* folios we're going to write back before we unlock them.
*/
void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
{
struct netfs_io_subrequest *subreq;
struct folio *folio;
unsigned int iopos, account = 0;
pgoff_t start_page = rreq->start / PAGE_SIZE;
pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
bool subreq_failed = false;
XA_STATE(xas, &rreq->mapping->i_pages, start_page);
if (test_bit(NETFS_RREQ_FAILED, &rreq->flags)) {
__clear_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
__clear_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
}
}
/* Walk through the pagecache and the I/O request lists simultaneously.
* We may have a mixture of cached and uncached sections and we only
* really want to write out the uncached sections. This is slightly
* complicated by the possibility that we might have huge pages with a
* mixture inside.
*/
subreq = list_first_entry(&rreq->subrequests,
struct netfs_io_subrequest, rreq_link);
iopos = 0;
subreq_failed = (subreq->error < 0);
trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
rcu_read_lock();
xas_for_each(&xas, folio, last_page) {
unsigned int pgpos = (folio_index(folio) - start_page) * PAGE_SIZE;
unsigned int pgend = pgpos + folio_size(folio);
bool pg_failed = false;
for (;;) {
if (!subreq) {
pg_failed = true;
break;
}
if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))
folio_start_fscache(folio);
pg_failed |= subreq_failed;
if (pgend < iopos + subreq->len)
break;
account += subreq->transferred;
iopos += subreq->len;
if (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
subreq = list_next_entry(subreq, rreq_link);
subreq_failed = (subreq->error < 0);
} else {
subreq = NULL;
subreq_failed = false;
}
if (pgend == iopos)
break;
}
if (!pg_failed) {
flush_dcache_folio(folio);
folio_mark_uptodate(folio);
}
if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
if (folio_index(folio) == rreq->no_unlock_folio &&
test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
_debug("no unlock");
else
folio_unlock(folio);
}
}
rcu_read_unlock();
task_io_account_read(account);
if (rreq->netfs_ops->done)
rreq->netfs_ops->done(rreq);
}
static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
loff_t *_start, size_t *_len, loff_t i_size)
{
struct netfs_cache_resources *cres = &rreq->cache_resources;
if (cres->ops && cres->ops->expand_readahead)
cres->ops->expand_readahead(cres, _start, _len, i_size);
}
static void netfs_rreq_expand(struct netfs_io_request *rreq,
struct readahead_control *ractl)
{
/* Give the cache a chance to change the request parameters. The
* resultant request must contain the original region.
*/
netfs_cache_expand_readahead(rreq, &rreq->start, &rreq->len, rreq->i_size);
/* Give the netfs a chance to change the request parameters. The
* resultant request must contain the original region.
*/
if (rreq->netfs_ops->expand_readahead)
rreq->netfs_ops->expand_readahead(rreq);
/* Expand the request if the cache wants it to start earlier. Note
* that the expansion may get further extended if the VM wishes to
* insert THPs and the preferred start and/or end wind up in the middle
* of THPs.
*
* If this is the case, however, the THP size should be an integer
* multiple of the cache granule size, so we get a whole number of
* granules to deal with.
*/
if (rreq->start != readahead_pos(ractl) ||
rreq->len != readahead_length(ractl)) {
readahead_expand(ractl, rreq->start, rreq->len);
rreq->start = readahead_pos(ractl);
rreq->len = readahead_length(ractl);
trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
netfs_read_trace_expanded);
}
}
/**
* netfs_readahead - Helper to manage a read request
* @ractl: The description of the readahead request
*
* Fulfil a readahead request by drawing data from the cache if possible, or
* the netfs if not. Space beyond the EOF is zero-filled. Multiple I/O
* requests from different sources will get munged together. If necessary, the
* readahead window can be expanded in either direction to a more convenient
* alighment for RPC efficiency or to make storage in the cache feasible.
*
* The calling netfs must initialise a netfs context contiguous to the vfs
* inode before calling this.
*
* This is usable whether or not caching is enabled.
*/
void netfs_readahead(struct readahead_control *ractl)
{
struct netfs_io_request *rreq;
struct netfs_inode *ctx = netfs_inode(ractl->mapping->host);
int ret;
_enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));
if (readahead_count(ractl) == 0)
return;
rreq = netfs_alloc_request(ractl->mapping, ractl->file,
readahead_pos(ractl),
readahead_length(ractl),
NETFS_READAHEAD);
if (IS_ERR(rreq))
return;
if (ctx->ops->begin_cache_operation) {
ret = ctx->ops->begin_cache_operation(rreq);
if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
goto cleanup_free;
}
netfs_stat(&netfs_n_rh_readahead);
trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
netfs_read_trace_readahead);
netfs_rreq_expand(rreq, ractl);
/* Drop the refs on the folios here rather than in the cache or
* filesystem. The locks will be dropped in netfs_rreq_unlock().
*/
while (readahead_folio(ractl))
;
netfs_begin_read(rreq, false);
return;
cleanup_free:
netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
return;
}
EXPORT_SYMBOL(netfs_readahead);
/**
* netfs_read_folio - Helper to manage a read_folio request
* @file: The file to read from
* @folio: The folio to read
*
* Fulfil a read_folio request by drawing data from the cache if
* possible, or the netfs if not. Space beyond the EOF is zero-filled.
* Multiple I/O requests from different sources will get munged together.
*
* The calling netfs must initialise a netfs context contiguous to the vfs
* inode before calling this.
*
* This is usable whether or not caching is enabled.
*/
int netfs_read_folio(struct file *file, struct folio *folio)
{
struct address_space *mapping = folio_file_mapping(folio);
struct netfs_io_request *rreq;
struct netfs_inode *ctx = netfs_inode(mapping->host);
int ret;
_enter("%lx", folio_index(folio));
rreq = netfs_alloc_request(mapping, file,
folio_file_pos(folio), folio_size(folio),
NETFS_READPAGE);
if (IS_ERR(rreq)) {
ret = PTR_ERR(rreq);
goto alloc_error;
}
if (ctx->ops->begin_cache_operation) {
ret = ctx->ops->begin_cache_operation(rreq);
if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
goto discard;
}
netfs_stat(&netfs_n_rh_readpage);
trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
return netfs_begin_read(rreq, true);
discard:
netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
alloc_error:
folio_unlock(folio);
return ret;
}
EXPORT_SYMBOL(netfs_read_folio);
/*
* Prepare a folio for writing without reading first
* @folio: The folio being prepared
* @pos: starting position for the write
* @len: length of write
* @always_fill: T if the folio should always be completely filled/cleared
*
* In some cases, write_begin doesn't need to read at all:
* - full folio write
* - write that lies in a folio that is completely beyond EOF
* - write that covers the folio from start to EOF or beyond it
*
* If any of these criteria are met, then zero out the unwritten parts
* of the folio and return true. Otherwise, return false.
*/
static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
bool always_fill)
{
struct inode *inode = folio_inode(folio);
loff_t i_size = i_size_read(inode);
size_t offset = offset_in_folio(folio, pos);
size_t plen = folio_size(folio);
if (unlikely(always_fill)) {
if (pos - offset + len <= i_size)
return false; /* Page entirely before EOF */
zero_user_segment(&folio->page, 0, plen);
folio_mark_uptodate(folio);
return true;
}
/* Full folio write */
if (offset == 0 && len >= plen)
return true;
/* Page entirely beyond the end of the file */
if (pos - offset >= i_size)
goto zero_out;
/* Write that covers from the start of the folio to EOF or beyond */
if (offset == 0 && (pos + len) >= i_size)
goto zero_out;
return false;
zero_out:
zero_user_segments(&folio->page, 0, offset, offset + len, plen);
return true;
}
/**
* netfs_write_begin - Helper to prepare for writing
* @ctx: The netfs context
* @file: The file to read from
* @mapping: The mapping to read from
* @pos: File position at which the write will begin
* @len: The length of the write (may extend beyond the end of the folio chosen)
* @_folio: Where to put the resultant folio
* @_fsdata: Place for the netfs to store a cookie
*
* Pre-read data for a write-begin request by drawing data from the cache if
* possible, or the netfs if not. Space beyond the EOF is zero-filled.
* Multiple I/O requests from different sources will get munged together. If
* necessary, the readahead window can be expanded in either direction to a
* more convenient alighment for RPC efficiency or to make storage in the cache
* feasible.
*
* The calling netfs must provide a table of operations, only one of which,
* issue_op, is mandatory.
*
* The check_write_begin() operation can be provided to check for and flush
* conflicting writes once the folio is grabbed and locked. It is passed a
* pointer to the fsdata cookie that gets returned to the VM to be passed to
* write_end. It is permitted to sleep. It should return 0 if the request
* should go ahead or it may return an error. It may also unlock and put the
* folio, provided it sets ``*foliop`` to NULL, in which case a return of 0
* will cause the folio to be re-got and the process to be retried.
*
* The calling netfs must initialise a netfs context contiguous to the vfs
* inode before calling this.
*
* This is usable whether or not caching is enabled.
*/
int netfs_write_begin(struct netfs_inode *ctx,
struct file *file, struct address_space *mapping,
loff_t pos, unsigned int len, struct folio **_folio,
void **_fsdata)
{
struct netfs_io_request *rreq;
struct folio *folio;
unsigned int fgp_flags = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE;
pgoff_t index = pos >> PAGE_SHIFT;
int ret;
DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
retry:
folio = __filemap_get_folio(mapping, index, fgp_flags,
mapping_gfp_mask(mapping));
if (!folio)
return -ENOMEM;
if (ctx->ops->check_write_begin) {
/* Allow the netfs (eg. ceph) to flush conflicts. */
ret = ctx->ops->check_write_begin(file, pos, len, &folio, _fsdata);
if (ret < 0) {
trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
goto error;
}
if (!folio)
goto retry;
}
if (folio_test_uptodate(folio))
goto have_folio;
/* If the page is beyond the EOF, we want to clear it - unless it's
* within the cache granule containing the EOF, in which case we need
* to preload the granule.
*/
if (!netfs_is_cache_enabled(ctx) &&
netfs_skip_folio_read(folio, pos, len, false)) {
netfs_stat(&netfs_n_rh_write_zskip);
goto have_folio_no_wait;
}
rreq = netfs_alloc_request(mapping, file,
folio_file_pos(folio), folio_size(folio),
NETFS_READ_FOR_WRITE);
if (IS_ERR(rreq)) {
ret = PTR_ERR(rreq);
goto error;
}
rreq->no_unlock_folio = folio_index(folio);
__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
if (ctx->ops->begin_cache_operation) {
ret = ctx->ops->begin_cache_operation(rreq);
if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
goto error_put;
}
netfs_stat(&netfs_n_rh_write_begin);
trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
/* Expand the request to meet caching requirements and download
* preferences.
*/
ractl._nr_pages = folio_nr_pages(folio);
netfs_rreq_expand(rreq, &ractl);
/* We hold the folio locks, so we can drop the references */
folio_get(folio);
while (readahead_folio(&ractl))
;
ret = netfs_begin_read(rreq, true);
if (ret < 0)
goto error;
have_folio:
ret = folio_wait_fscache_killable(folio);
if (ret < 0)
goto error;
have_folio_no_wait:
*_folio = folio;
_leave(" = 0");
return 0;
error_put:
netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
error:
if (folio) {
folio_unlock(folio);
folio_put(folio);
}
_leave(" = %d", ret);
return ret;
}
EXPORT_SYMBOL(netfs_write_begin);