linuxdebug/fs/netfs/io.c

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2024-07-16 15:50:57 +02:00
// SPDX-License-Identifier: GPL-2.0-or-later
/* Network filesystem high-level read support.
*
* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#include <linux/module.h>
#include <linux/export.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/uio.h>
#include <linux/sched/mm.h>
#include <linux/task_io_accounting_ops.h>
#include "internal.h"
/*
* Clear the unread part of an I/O request.
*/
static void netfs_clear_unread(struct netfs_io_subrequest *subreq)
{
struct iov_iter iter;
iov_iter_xarray(&iter, ITER_DEST, &subreq->rreq->mapping->i_pages,
subreq->start + subreq->transferred,
subreq->len - subreq->transferred);
iov_iter_zero(iov_iter_count(&iter), &iter);
}
static void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error,
bool was_async)
{
struct netfs_io_subrequest *subreq = priv;
netfs_subreq_terminated(subreq, transferred_or_error, was_async);
}
/*
* Issue a read against the cache.
* - Eats the caller's ref on subreq.
*/
static void netfs_read_from_cache(struct netfs_io_request *rreq,
struct netfs_io_subrequest *subreq,
enum netfs_read_from_hole read_hole)
{
struct netfs_cache_resources *cres = &rreq->cache_resources;
struct iov_iter iter;
netfs_stat(&netfs_n_rh_read);
iov_iter_xarray(&iter, ITER_DEST, &rreq->mapping->i_pages,
subreq->start + subreq->transferred,
subreq->len - subreq->transferred);
cres->ops->read(cres, subreq->start, &iter, read_hole,
netfs_cache_read_terminated, subreq);
}
/*
* Fill a subrequest region with zeroes.
*/
static void netfs_fill_with_zeroes(struct netfs_io_request *rreq,
struct netfs_io_subrequest *subreq)
{
netfs_stat(&netfs_n_rh_zero);
__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
netfs_subreq_terminated(subreq, 0, false);
}
/*
* Ask the netfs to issue a read request to the server for us.
*
* The netfs is expected to read from subreq->pos + subreq->transferred to
* subreq->pos + subreq->len - 1. It may not backtrack and write data into the
* buffer prior to the transferred point as it might clobber dirty data
* obtained from the cache.
*
* Alternatively, the netfs is allowed to indicate one of two things:
*
* - NETFS_SREQ_SHORT_READ: A short read - it will get called again to try and
* make progress.
*
* - NETFS_SREQ_CLEAR_TAIL: A short read - the rest of the buffer will be
* cleared.
*/
static void netfs_read_from_server(struct netfs_io_request *rreq,
struct netfs_io_subrequest *subreq)
{
netfs_stat(&netfs_n_rh_download);
rreq->netfs_ops->issue_read(subreq);
}
/*
* Release those waiting.
*/
static void netfs_rreq_completed(struct netfs_io_request *rreq, bool was_async)
{
trace_netfs_rreq(rreq, netfs_rreq_trace_done);
netfs_clear_subrequests(rreq, was_async);
netfs_put_request(rreq, was_async, netfs_rreq_trace_put_complete);
}
/*
* Deal with the completion of writing the data to the cache. We have to clear
* the PG_fscache bits on the folios involved and release the caller's ref.
*
* May be called in softirq mode and we inherit a ref from the caller.
*/
static void netfs_rreq_unmark_after_write(struct netfs_io_request *rreq,
bool was_async)
{
struct netfs_io_subrequest *subreq;
struct folio *folio;
pgoff_t unlocked = 0;
bool have_unlocked = false;
rcu_read_lock();
list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
XA_STATE(xas, &rreq->mapping->i_pages, subreq->start / PAGE_SIZE);
xas_for_each(&xas, folio, (subreq->start + subreq->len - 1) / PAGE_SIZE) {
if (xas_retry(&xas, folio))
continue;
/* We might have multiple writes from the same huge
* folio, but we mustn't unlock a folio more than once.
*/
if (have_unlocked && folio_index(folio) <= unlocked)
continue;
unlocked = folio_index(folio);
folio_end_fscache(folio);
have_unlocked = true;
}
}
rcu_read_unlock();
netfs_rreq_completed(rreq, was_async);
}
static void netfs_rreq_copy_terminated(void *priv, ssize_t transferred_or_error,
bool was_async)
{
struct netfs_io_subrequest *subreq = priv;
struct netfs_io_request *rreq = subreq->rreq;
if (IS_ERR_VALUE(transferred_or_error)) {
netfs_stat(&netfs_n_rh_write_failed);
trace_netfs_failure(rreq, subreq, transferred_or_error,
netfs_fail_copy_to_cache);
} else {
netfs_stat(&netfs_n_rh_write_done);
}
trace_netfs_sreq(subreq, netfs_sreq_trace_write_term);
/* If we decrement nr_copy_ops to 0, the ref belongs to us. */
if (atomic_dec_and_test(&rreq->nr_copy_ops))
netfs_rreq_unmark_after_write(rreq, was_async);
netfs_put_subrequest(subreq, was_async, netfs_sreq_trace_put_terminated);
}
/*
* Perform any outstanding writes to the cache. We inherit a ref from the
* caller.
*/
static void netfs_rreq_do_write_to_cache(struct netfs_io_request *rreq)
{
struct netfs_cache_resources *cres = &rreq->cache_resources;
struct netfs_io_subrequest *subreq, *next, *p;
struct iov_iter iter;
int ret;
trace_netfs_rreq(rreq, netfs_rreq_trace_copy);
/* We don't want terminating writes trying to wake us up whilst we're
* still going through the list.
*/
atomic_inc(&rreq->nr_copy_ops);
list_for_each_entry_safe(subreq, p, &rreq->subrequests, rreq_link) {
if (!test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) {
list_del_init(&subreq->rreq_link);
netfs_put_subrequest(subreq, false,
netfs_sreq_trace_put_no_copy);
}
}
list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
/* Amalgamate adjacent writes */
while (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
next = list_next_entry(subreq, rreq_link);
if (next->start != subreq->start + subreq->len)
break;
subreq->len += next->len;
list_del_init(&next->rreq_link);
netfs_put_subrequest(next, false,
netfs_sreq_trace_put_merged);
}
ret = cres->ops->prepare_write(cres, &subreq->start, &subreq->len,
rreq->i_size, true);
if (ret < 0) {
trace_netfs_failure(rreq, subreq, ret, netfs_fail_prepare_write);
trace_netfs_sreq(subreq, netfs_sreq_trace_write_skip);
continue;
}
iov_iter_xarray(&iter, ITER_SOURCE, &rreq->mapping->i_pages,
subreq->start, subreq->len);
atomic_inc(&rreq->nr_copy_ops);
netfs_stat(&netfs_n_rh_write);
netfs_get_subrequest(subreq, netfs_sreq_trace_get_copy_to_cache);
trace_netfs_sreq(subreq, netfs_sreq_trace_write);
cres->ops->write(cres, subreq->start, &iter,
netfs_rreq_copy_terminated, subreq);
}
/* If we decrement nr_copy_ops to 0, the usage ref belongs to us. */
if (atomic_dec_and_test(&rreq->nr_copy_ops))
netfs_rreq_unmark_after_write(rreq, false);
}
static void netfs_rreq_write_to_cache_work(struct work_struct *work)
{
struct netfs_io_request *rreq =
container_of(work, struct netfs_io_request, work);
netfs_rreq_do_write_to_cache(rreq);
}
static void netfs_rreq_write_to_cache(struct netfs_io_request *rreq)
{
rreq->work.func = netfs_rreq_write_to_cache_work;
if (!queue_work(system_unbound_wq, &rreq->work))
BUG();
}
/*
* Handle a short read.
*/
static void netfs_rreq_short_read(struct netfs_io_request *rreq,
struct netfs_io_subrequest *subreq)
{
__clear_bit(NETFS_SREQ_SHORT_IO, &subreq->flags);
__set_bit(NETFS_SREQ_SEEK_DATA_READ, &subreq->flags);
netfs_stat(&netfs_n_rh_short_read);
trace_netfs_sreq(subreq, netfs_sreq_trace_resubmit_short);
netfs_get_subrequest(subreq, netfs_sreq_trace_get_short_read);
atomic_inc(&rreq->nr_outstanding);
if (subreq->source == NETFS_READ_FROM_CACHE)
netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_CLEAR);
else
netfs_read_from_server(rreq, subreq);
}
/*
* Resubmit any short or failed operations. Returns true if we got the rreq
* ref back.
*/
static bool netfs_rreq_perform_resubmissions(struct netfs_io_request *rreq)
{
struct netfs_io_subrequest *subreq;
WARN_ON(in_interrupt());
trace_netfs_rreq(rreq, netfs_rreq_trace_resubmit);
/* We don't want terminating submissions trying to wake us up whilst
* we're still going through the list.
*/
atomic_inc(&rreq->nr_outstanding);
__clear_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
if (subreq->error) {
if (subreq->source != NETFS_READ_FROM_CACHE)
break;
subreq->source = NETFS_DOWNLOAD_FROM_SERVER;
subreq->error = 0;
netfs_stat(&netfs_n_rh_download_instead);
trace_netfs_sreq(subreq, netfs_sreq_trace_download_instead);
netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
atomic_inc(&rreq->nr_outstanding);
netfs_read_from_server(rreq, subreq);
} else if (test_bit(NETFS_SREQ_SHORT_IO, &subreq->flags)) {
netfs_rreq_short_read(rreq, subreq);
}
}
/* If we decrement nr_outstanding to 0, the usage ref belongs to us. */
if (atomic_dec_and_test(&rreq->nr_outstanding))
return true;
wake_up_var(&rreq->nr_outstanding);
return false;
}
/*
* Check to see if the data read is still valid.
*/
static void netfs_rreq_is_still_valid(struct netfs_io_request *rreq)
{
struct netfs_io_subrequest *subreq;
if (!rreq->netfs_ops->is_still_valid ||
rreq->netfs_ops->is_still_valid(rreq))
return;
list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
if (subreq->source == NETFS_READ_FROM_CACHE) {
subreq->error = -ESTALE;
__set_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
}
}
}
/*
* Assess the state of a read request and decide what to do next.
*
* Note that we could be in an ordinary kernel thread, on a workqueue or in
* softirq context at this point. We inherit a ref from the caller.
*/
static void netfs_rreq_assess(struct netfs_io_request *rreq, bool was_async)
{
trace_netfs_rreq(rreq, netfs_rreq_trace_assess);
again:
netfs_rreq_is_still_valid(rreq);
if (!test_bit(NETFS_RREQ_FAILED, &rreq->flags) &&
test_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags)) {
if (netfs_rreq_perform_resubmissions(rreq))
goto again;
return;
}
netfs_rreq_unlock_folios(rreq);
clear_bit_unlock(NETFS_RREQ_IN_PROGRESS, &rreq->flags);
wake_up_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS);
if (test_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags))
return netfs_rreq_write_to_cache(rreq);
netfs_rreq_completed(rreq, was_async);
}
static void netfs_rreq_work(struct work_struct *work)
{
struct netfs_io_request *rreq =
container_of(work, struct netfs_io_request, work);
netfs_rreq_assess(rreq, false);
}
/*
* Handle the completion of all outstanding I/O operations on a read request.
* We inherit a ref from the caller.
*/
static void netfs_rreq_terminated(struct netfs_io_request *rreq,
bool was_async)
{
if (test_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags) &&
was_async) {
if (!queue_work(system_unbound_wq, &rreq->work))
BUG();
} else {
netfs_rreq_assess(rreq, was_async);
}
}
/**
* netfs_subreq_terminated - Note the termination of an I/O operation.
* @subreq: The I/O request that has terminated.
* @transferred_or_error: The amount of data transferred or an error code.
* @was_async: The termination was asynchronous
*
* This tells the read helper that a contributory I/O operation has terminated,
* one way or another, and that it should integrate the results.
*
* The caller indicates in @transferred_or_error the outcome of the operation,
* supplying a positive value to indicate the number of bytes transferred, 0 to
* indicate a failure to transfer anything that should be retried or a negative
* error code. The helper will look after reissuing I/O operations as
* appropriate and writing downloaded data to the cache.
*
* If @was_async is true, the caller might be running in softirq or interrupt
* context and we can't sleep.
*/
void netfs_subreq_terminated(struct netfs_io_subrequest *subreq,
ssize_t transferred_or_error,
bool was_async)
{
struct netfs_io_request *rreq = subreq->rreq;
int u;
_enter("[%u]{%llx,%lx},%zd",
subreq->debug_index, subreq->start, subreq->flags,
transferred_or_error);
switch (subreq->source) {
case NETFS_READ_FROM_CACHE:
netfs_stat(&netfs_n_rh_read_done);
break;
case NETFS_DOWNLOAD_FROM_SERVER:
netfs_stat(&netfs_n_rh_download_done);
break;
default:
break;
}
if (IS_ERR_VALUE(transferred_or_error)) {
subreq->error = transferred_or_error;
trace_netfs_failure(rreq, subreq, transferred_or_error,
netfs_fail_read);
goto failed;
}
if (WARN(transferred_or_error > subreq->len - subreq->transferred,
"Subreq overread: R%x[%x] %zd > %zu - %zu",
rreq->debug_id, subreq->debug_index,
transferred_or_error, subreq->len, subreq->transferred))
transferred_or_error = subreq->len - subreq->transferred;
subreq->error = 0;
subreq->transferred += transferred_or_error;
if (subreq->transferred < subreq->len)
goto incomplete;
complete:
__clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))
set_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
out:
trace_netfs_sreq(subreq, netfs_sreq_trace_terminated);
/* If we decrement nr_outstanding to 0, the ref belongs to us. */
u = atomic_dec_return(&rreq->nr_outstanding);
if (u == 0)
netfs_rreq_terminated(rreq, was_async);
else if (u == 1)
wake_up_var(&rreq->nr_outstanding);
netfs_put_subrequest(subreq, was_async, netfs_sreq_trace_put_terminated);
return;
incomplete:
if (test_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags)) {
netfs_clear_unread(subreq);
subreq->transferred = subreq->len;
goto complete;
}
if (transferred_or_error == 0) {
if (__test_and_set_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags)) {
subreq->error = -ENODATA;
goto failed;
}
} else {
__clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
}
__set_bit(NETFS_SREQ_SHORT_IO, &subreq->flags);
set_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
goto out;
failed:
if (subreq->source == NETFS_READ_FROM_CACHE) {
netfs_stat(&netfs_n_rh_read_failed);
set_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
} else {
netfs_stat(&netfs_n_rh_download_failed);
set_bit(NETFS_RREQ_FAILED, &rreq->flags);
rreq->error = subreq->error;
}
goto out;
}
EXPORT_SYMBOL(netfs_subreq_terminated);
static enum netfs_io_source netfs_cache_prepare_read(struct netfs_io_subrequest *subreq,
loff_t i_size)
{
struct netfs_io_request *rreq = subreq->rreq;
struct netfs_cache_resources *cres = &rreq->cache_resources;
if (cres->ops)
return cres->ops->prepare_read(subreq, i_size);
if (subreq->start >= rreq->i_size)
return NETFS_FILL_WITH_ZEROES;
return NETFS_DOWNLOAD_FROM_SERVER;
}
/*
* Work out what sort of subrequest the next one will be.
*/
static enum netfs_io_source
netfs_rreq_prepare_read(struct netfs_io_request *rreq,
struct netfs_io_subrequest *subreq)
{
enum netfs_io_source source;
_enter("%llx-%llx,%llx", subreq->start, subreq->start + subreq->len, rreq->i_size);
source = netfs_cache_prepare_read(subreq, rreq->i_size);
if (source == NETFS_INVALID_READ)
goto out;
if (source == NETFS_DOWNLOAD_FROM_SERVER) {
/* Call out to the netfs to let it shrink the request to fit
* its own I/O sizes and boundaries. If it shinks it here, it
* will be called again to make simultaneous calls; if it wants
* to make serial calls, it can indicate a short read and then
* we will call it again.
*/
if (subreq->len > rreq->i_size - subreq->start)
subreq->len = rreq->i_size - subreq->start;
if (rreq->netfs_ops->clamp_length &&
!rreq->netfs_ops->clamp_length(subreq)) {
source = NETFS_INVALID_READ;
goto out;
}
}
if (WARN_ON(subreq->len == 0))
source = NETFS_INVALID_READ;
out:
subreq->source = source;
trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
return source;
}
/*
* Slice off a piece of a read request and submit an I/O request for it.
*/
static bool netfs_rreq_submit_slice(struct netfs_io_request *rreq,
unsigned int *_debug_index)
{
struct netfs_io_subrequest *subreq;
enum netfs_io_source source;
subreq = netfs_alloc_subrequest(rreq);
if (!subreq)
return false;
subreq->debug_index = (*_debug_index)++;
subreq->start = rreq->start + rreq->submitted;
subreq->len = rreq->len - rreq->submitted;
_debug("slice %llx,%zx,%zx", subreq->start, subreq->len, rreq->submitted);
list_add_tail(&subreq->rreq_link, &rreq->subrequests);
/* Call out to the cache to find out what it can do with the remaining
* subset. It tells us in subreq->flags what it decided should be done
* and adjusts subreq->len down if the subset crosses a cache boundary.
*
* Then when we hand the subset, it can choose to take a subset of that
* (the starts must coincide), in which case, we go around the loop
* again and ask it to download the next piece.
*/
source = netfs_rreq_prepare_read(rreq, subreq);
if (source == NETFS_INVALID_READ)
goto subreq_failed;
atomic_inc(&rreq->nr_outstanding);
rreq->submitted += subreq->len;
trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
switch (source) {
case NETFS_FILL_WITH_ZEROES:
netfs_fill_with_zeroes(rreq, subreq);
break;
case NETFS_DOWNLOAD_FROM_SERVER:
netfs_read_from_server(rreq, subreq);
break;
case NETFS_READ_FROM_CACHE:
netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_IGNORE);
break;
default:
BUG();
}
return true;
subreq_failed:
rreq->error = subreq->error;
netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_failed);
return false;
}
/*
* Begin the process of reading in a chunk of data, where that data may be
* stitched together from multiple sources, including multiple servers and the
* local cache.
*/
int netfs_begin_read(struct netfs_io_request *rreq, bool sync)
{
unsigned int debug_index = 0;
int ret;
_enter("R=%x %llx-%llx",
rreq->debug_id, rreq->start, rreq->start + rreq->len - 1);
if (rreq->len == 0) {
pr_err("Zero-sized read [R=%x]\n", rreq->debug_id);
netfs_put_request(rreq, false, netfs_rreq_trace_put_zero_len);
return -EIO;
}
INIT_WORK(&rreq->work, netfs_rreq_work);
if (sync)
netfs_get_request(rreq, netfs_rreq_trace_get_hold);
/* Chop the read into slices according to what the cache and the netfs
* want and submit each one.
*/
atomic_set(&rreq->nr_outstanding, 1);
do {
if (!netfs_rreq_submit_slice(rreq, &debug_index))
break;
} while (rreq->submitted < rreq->len);
if (sync) {
/* Keep nr_outstanding incremented so that the ref always belongs to
* us, and the service code isn't punted off to a random thread pool to
* process.
*/
for (;;) {
wait_var_event(&rreq->nr_outstanding,
atomic_read(&rreq->nr_outstanding) == 1);
netfs_rreq_assess(rreq, false);
if (!test_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags))
break;
cond_resched();
}
ret = rreq->error;
if (ret == 0 && rreq->submitted < rreq->len) {
trace_netfs_failure(rreq, NULL, ret, netfs_fail_short_read);
ret = -EIO;
}
netfs_put_request(rreq, false, netfs_rreq_trace_put_hold);
} else {
/* If we decrement nr_outstanding to 0, the ref belongs to us. */
if (atomic_dec_and_test(&rreq->nr_outstanding))
netfs_rreq_assess(rreq, false);
ret = 0;
}
return ret;
}