netfs: Fix a number of read-retry hangs

This patch should better fix the hangs that have been seen than Ihor's previously tested fix (which I think isn't actually correct). David Signed-off-by: Steve French <[email protected]>
smfrench · Feb 12, 2025 · 9a08afe · 9a08afe
1 parent f2251cd
commit 9a08afe
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Showing 4 changed files with 38 additions and 14 deletions.
diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
@@ -470,7 +470,8 @@ void netfs_read_collection_worker(struct work_struct *work)
  */
 void netfs_wake_read_collector(struct netfs_io_request *rreq)
 {
-	if (test_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &rreq->flags)) {
+	if (test_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &rreq->flags) &&
+	    !test_bit(NETFS_RREQ_RETRYING, &rreq->flags)) {
 		if (!work_pending(&rreq->work)) {
 			netfs_get_request(rreq, netfs_rreq_trace_get_work);
 			if (!queue_work(system_unbound_wq, &rreq->work))
@@ -586,7 +587,8 @@ void netfs_read_subreq_terminated(struct netfs_io_subrequest *subreq)
 	smp_mb__after_atomic(); /* Clear IN_PROGRESS before task state */
 
 	/* If we are at the head of the queue, wake up the collector. */
-	if (list_is_first(&subreq->rreq_link, &stream->subrequests))
+	if (list_is_first(&subreq->rreq_link, &stream->subrequests) ||
+	    test_bit(NETFS_RREQ_RETRYING, &rreq->flags))
 		netfs_wake_read_collector(rreq);
 
 	netfs_put_subrequest(subreq, true, netfs_sreq_trace_put_terminated);

diff --git a/fs/netfs/read_retry.c b/fs/netfs/read_retry.c
@@ -14,7 +14,6 @@ static void netfs_reissue_read(struct netfs_io_request *rreq,
 {
 	__clear_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
 	__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
-	netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
 	subreq->rreq->netfs_ops->issue_read(subreq);
 }
 
@@ -48,6 +47,7 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
 				__clear_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
 				subreq->retry_count++;
 				netfs_reset_iter(subreq);
+				netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
 				netfs_reissue_read(rreq, subreq);
 			}
 		}
@@ -75,7 +75,7 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
 		struct iov_iter source;
 		unsigned long long start, len;
 		size_t part;
-		bool boundary = false;
+		bool boundary = false, subreq_superfluous = false;
 
 		/* Go through the subreqs and find the next span of contiguous
 		 * buffer that we then rejig (cifs, for example, needs the
@@ -116,8 +116,10 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
 		/* Work through the sublist. */
 		subreq = from;
 		list_for_each_entry_from(subreq, &stream->subrequests, rreq_link) {
-			if (!len)
+			if (!len) {
+				subreq_superfluous = true;
 				break;
+			}
 			subreq->source	= NETFS_DOWNLOAD_FROM_SERVER;
 			subreq->start	= start - subreq->transferred;
 			subreq->len	= len   + subreq->transferred;
@@ -154,19 +156,21 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
 
 			netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
 			netfs_reissue_read(rreq, subreq);
-			if (subreq == to)
+			if (subreq == to) {
+				subreq_superfluous = false;
 				break;
+			}
 		}
 
 		/* If we managed to use fewer subreqs, we can discard the
 		 * excess; if we used the same number, then we're done.
 		 */
 		if (!len) {
-			if (subreq == to)
+			if (!subreq_superfluous)
 				continue;
 			list_for_each_entry_safe_from(subreq, tmp,
 						      &stream->subrequests, rreq_link) {
-				trace_netfs_sreq(subreq, netfs_sreq_trace_discard);
+				trace_netfs_sreq(subreq, netfs_sreq_trace_superfluous);
 				list_del(&subreq->rreq_link);
 				netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_done);
 				if (subreq == to)
@@ -187,14 +191,12 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
 			subreq->source		= NETFS_DOWNLOAD_FROM_SERVER;
 			subreq->start		= start;
 			subreq->len		= len;
-			subreq->debug_index	= atomic_inc_return(&rreq->subreq_counter);
 			subreq->stream_nr	= stream->stream_nr;
 			subreq->retry_count	= 1;
 
 			trace_netfs_sreq_ref(rreq->debug_id, subreq->debug_index,
 					     refcount_read(&subreq->ref),
 					     netfs_sreq_trace_new);
-			netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
 
 			list_add(&subreq->rreq_link, &to->rreq_link);
 			to = list_next_entry(to, rreq_link);
@@ -256,14 +258,32 @@ void netfs_retry_reads(struct netfs_io_request *rreq)
 {
 	struct netfs_io_subrequest *subreq;
 	struct netfs_io_stream *stream = &rreq->io_streams[0];
+	DEFINE_WAIT(myself);
+
+	set_bit(NETFS_RREQ_RETRYING, &rreq->flags);
 
 	/* Wait for all outstanding I/O to quiesce before performing retries as
 	 * we may need to renegotiate the I/O sizes.
 	 */
 	list_for_each_entry(subreq, &stream->subrequests, rreq_link) {
-		wait_on_bit(&subreq->flags, NETFS_SREQ_IN_PROGRESS,
-			    TASK_UNINTERRUPTIBLE);
+		if (!test_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags))
+			continue;
+
+		trace_netfs_rreq(rreq, netfs_rreq_trace_wait_queue);
+		for (;;) {
+			prepare_to_wait(&rreq->waitq, &myself, TASK_UNINTERRUPTIBLE);
+
+			if (!test_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags))
+				break;
+
+			trace_netfs_sreq(subreq, netfs_sreq_trace_wait_for);
+			schedule();
+			trace_netfs_rreq(rreq, netfs_rreq_trace_woke_queue);
+		}
+
+		finish_wait(&rreq->waitq, &myself);
 	}
+	clear_bit(NETFS_RREQ_RETRYING, &rreq->flags);
 
 	trace_netfs_rreq(rreq, netfs_rreq_trace_resubmit);
 	netfs_retry_read_subrequests(rreq);

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
@@ -278,7 +278,7 @@ struct netfs_io_request {
 #define NETFS_RREQ_PAUSE		11	/* Pause subrequest generation */
 #define NETFS_RREQ_USE_IO_ITER		12	/* Use ->io_iter rather than ->i_pages */
 #define NETFS_RREQ_ALL_QUEUED		13	/* All subreqs are now queued */
-#define NETFS_RREQ_NEED_RETRY		14	/* Need to try retrying */
+#define NETFS_RREQ_RETRYING		14	/* Set if we're in the retry path */
 #define NETFS_RREQ_USE_PGPRIV2		31	/* [DEPRECATED] Use PG_private_2 to mark
 						 * write to cache on read */
 	const struct netfs_request_ops *netfs_ops;

diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
@@ -99,7 +99,7 @@
 	EM(netfs_sreq_trace_limited,		"LIMIT")	\
 	EM(netfs_sreq_trace_need_clear,		"N-CLR")	\
 	EM(netfs_sreq_trace_partial_read,	"PARTR")	\
-	EM(netfs_sreq_trace_need_retry,		"NRTRY")	\
+	EM(netfs_sreq_trace_need_retry,		"ND-RT")	\
 	EM(netfs_sreq_trace_prepare,		"PREP ")	\
 	EM(netfs_sreq_trace_prep_failed,	"PRPFL")	\
 	EM(netfs_sreq_trace_progress,		"PRGRS")	\
@@ -108,7 +108,9 @@
 	EM(netfs_sreq_trace_short,		"SHORT")	\
 	EM(netfs_sreq_trace_split,		"SPLIT")	\
 	EM(netfs_sreq_trace_submit,		"SUBMT")	\
+	EM(netfs_sreq_trace_superfluous,	"SPRFL")	\
 	EM(netfs_sreq_trace_terminated,		"TERM ")	\
+	EM(netfs_sreq_trace_wait_for,		"_WAIT")	\
 	EM(netfs_sreq_trace_write,		"WRITE")	\
 	EM(netfs_sreq_trace_write_skip,		"SKIP ")	\
 	E_(netfs_sreq_trace_write_term,		"WTERM")