linux-kernel - [PATCH 3.16 63/87] btrfs: start readahead also in seed devices

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Message-ID: <lsq.1570043211.469797181@decadent.org.uk>
Date:   Wed, 02 Oct 2019 20:06:51 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Naohiro Aota" <naohiro.aota@....com>,
        "David Sterba" <dsterba@...e.com>,
        "Filipe Manana" <fdmanana@...e.com>
Subject: [PATCH 3.16 63/87] btrfs: start readahead also in seed devices

3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Naohiro Aota <naohiro.aota@....com>

commit c4e0540d0ad49c8ceab06cceed1de27c4fe29f6e upstream.

Currently, btrfs does not consult seed devices to start readahead. As a
result, if readahead zone is added to the seed devices, btrfs_reada_wait()
indefinitely wait for the reada_ctl to finish.

You can reproduce the hung by modifying btrfs/163 to have larger initial
file size (e.g. xfs_io pwrite 4M instead of current 256K).

Fixes: 7414a03fbf9e ("btrfs: initial readahead code and prototypes")
Reviewed-by: Filipe Manana <fdmanana@...e.com>
Signed-off-by: Naohiro Aota <naohiro.aota@....com>
Signed-off-by: David Sterba <dsterba@...e.com>
---
 fs/btrfs/reada.c | 5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -764,6 +764,7 @@ static void __reada_start_machine(struct
 	u64 total = 0;
 	int i;
 
+again:
 	do {
 		enqueued = 0;
 		mutex_lock(&fs_devices->device_list_mutex);
@@ -776,6 +777,10 @@ static void __reada_start_machine(struct
 		mutex_unlock(&fs_devices->device_list_mutex);
 		total += enqueued;
 	} while (enqueued && total < 10000);
+	if (fs_devices->seed) {
+		fs_devices = fs_devices->seed;
+		goto again;
+	}
 
 	if (enqueued == 0)
 		return;