[PATCH v5 22/40] netfs: Make the refcounting of netfs_begin_read() easier to use

David Howells
2023-12-21T13:25:37Z

Make the refcounting of netfs_begin_read() easier to use by not eating the
caller's ref on the netfs_io_request it's given. This makes it easier to
use when we need to look in the request struct after.

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
---
fs/netfs/buffered_read.c | 6 +++++-
fs/netfs/io.c | 28 +++++++++++++---------------
include/trace/events/netfs.h | 9 +++++----
3 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index 751556faa70b..6b9a44cafbac 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -210,6 +210,7 @@ void netfs_readahead(struct readahead_control *ractl)
;

netfs_begin_read(rreq, false);
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
return;

cleanup_free:
@@ -260,7 +261,9 @@ int netfs_read_folio(struct file *file, struct folio *folio)
iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
rreq->start, rreq->len);

- return netfs_begin_read(rreq, true);
+ ret = netfs_begin_read(rreq, true);
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
+ return ret;

discard:
netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
@@ -429,6 +432,7 @@ int netfs_write_begin(struct netfs_inode *ctx,
ret = netfs_begin_read(rreq, true);
if (ret < 0)
goto error;
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_return);

have_folio:
ret = folio_wait_fscache_killable(folio);
diff --git a/fs/netfs/io.c b/fs/netfs/io.c
index e228bfb530ea..e83ef5835d25 100644
--- a/fs/netfs/io.c
+++ b/fs/netfs/io.c
@@ -362,6 +362,7 @@ static void netfs_rreq_assess(struct netfs_io_request *rreq, bool was_async)

netfs_rreq_unlock_folios(rreq);

+ trace_netfs_rreq(rreq, netfs_rreq_trace_wake_ip);
clear_bit_unlock(NETFS_RREQ_IN_PROGRESS, &rreq->flags);
wake_up_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS);

@@ -657,7 +658,6 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync)

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;
}

@@ -665,12 +665,10 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync)

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.
*/
+ netfs_get_request(rreq, netfs_rreq_trace_get_for_outstanding);
atomic_set(&rreq->nr_outstanding, 1);
io_iter = rreq->io_iter;
do {
@@ -680,25 +678,25 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync)
} 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.
+ /* 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. Note that this might start
+ * further work, such as writing to the cache.
*/
- for (;;) {
- wait_var_event(&rreq->nr_outstanding,
- atomic_read(&rreq->nr_outstanding) == 1);
+ wait_var_event(&rreq->nr_outstanding,
+ atomic_read(&rreq->nr_outstanding) == 1);
+ if (atomic_dec_and_test(&rreq->nr_outstanding))
netfs_rreq_assess(rreq, false);
- if (!test_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags))
- break;
- cond_resched();
- }
+
+ trace_netfs_rreq(rreq, netfs_rreq_trace_wait_ip);
+ wait_on_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS,
+ TASK_UNINTERRUPTIBLE);

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))
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 4ea4e34d279f..6daadf2aac8a 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -34,7 +34,9 @@
EM(netfs_rreq_trace_free, "FREE ") \
EM(netfs_rreq_trace_resubmit, "RESUBMT") \
EM(netfs_rreq_trace_unlock, "UNLOCK ") \
- E_(netfs_rreq_trace_unmark, "UNMARK ")
+ EM(netfs_rreq_trace_unmark, "UNMARK ") \
+ EM(netfs_rreq_trace_wait_ip, "WAIT-IP") \
+ E_(netfs_rreq_trace_wake_ip, "WAKE-IP")

#define netfs_sreq_sources \
EM(NETFS_FILL_WITH_ZEROES, "ZERO") \
@@ -65,14 +67,13 @@
E_(netfs_fail_prepare_write, "prep-write")

#define netfs_rreq_ref_traces \
- EM(netfs_rreq_trace_get_hold, "GET HOLD ") \
+ EM(netfs_rreq_trace_get_for_outstanding,"GET OUTSTND") \
EM(netfs_rreq_trace_get_subreq, "GET SUBREQ ") \
EM(netfs_rreq_trace_put_complete, "PUT COMPLT ") \
EM(netfs_rreq_trace_put_discard, "PUT DISCARD") \
EM(netfs_rreq_trace_put_failed, "PUT FAILED ") \
- EM(netfs_rreq_trace_put_hold, "PUT HOLD ") \
+ EM(netfs_rreq_trace_put_return, "PUT RETURN ") \
EM(netfs_rreq_trace_put_subreq, "PUT SUBREQ ") \
- EM(netfs_rreq_trace_put_zero_len, "PUT ZEROLEN") \
E_(netfs_rreq_trace_new, "NEW ")

#define netfs_sreq_ref_traces \