linux-kernel - [PATCH] afs: Fix fileserver probe RTT handling

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Date:   Mon, 28 Nov 2022 22:02:56 +0000
From:   David Howells <dhowells@...hat.com>
To:     torvalds@...ux-foundation.org
cc:     dhowells@...hat.com, marc.dionne@...istor.com,
        linux-afs@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] afs: Fix fileserver probe RTT handling

Hi Linus,

Could you apply this patch, please?

Thanks,
David
---
The fileserver probing code attempts to work out the best fileserver to use
for a volume by retrieving the RTT calculated by AF_RXRPC for the probe
call sent to each server and comparing them.  Sometimes, however, no RTT
estimate is available and rxrpc_kernel_get_srtt() returns false, leading
good fileservers to be given an RTT of UINT_MAX and thus causing the
rotation algorithm to ignore them.

Fix afs_select_fileserver() to ignore rxrpc_kernel_get_srtt()'s return
value and just take the estimated RTT it provides - which will be capped at
1 second.

Fixes: 1d4adfaf6574 ("rxrpc: Make rxrpc_kernel_get_srtt() indicate validity")
Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: Marc Dionne <marc.dionne@...istor.com>
Tested-by: Marc Dionne <marc.dionne@...istor.com>
cc: linux-afs@...ts.infradead.org
Link: https://lore.kernel.org/r/166965503999.3392585.13954054113218099395.stgit@warthog.procyon.org.uk/
---
 fs/afs/fs_probe.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/afs/fs_probe.c b/fs/afs/fs_probe.c
index c0031a3ab42f..3ac5fcf98d0d 100644
--- a/fs/afs/fs_probe.c
+++ b/fs/afs/fs_probe.c
@@ -167,8 +167,8 @@ void afs_fileserver_probe_result(struct afs_call *call)
 			clear_bit(AFS_SERVER_FL_HAS_FS64, &server->flags);
 	}
 
-	if (rxrpc_kernel_get_srtt(call->net->socket, call->rxcall, &rtt_us) &&
-	    rtt_us < server->probe.rtt) {
+	rxrpc_kernel_get_srtt(call->net->socket, call->rxcall, &rtt_us);
+	if (rtt_us < server->probe.rtt) {
 		server->probe.rtt = rtt_us;
 		server->rtt = rtt_us;
 		alist->preferred = index;