[SRU][J:linux-bluefield][PATCH 0/1] Bluefield 5.15.0-1084.86 build failure: nfsd4_get_drc_mem assertion with GCC 9

[Satya Jhaveri]

From: NeilBrown <neil at brown.name>

BugLink: https://bugs.launchpad.net/bugs/2142422

A recent change to clamp_t() in 6.1.y caused fs/nfsd/nfs4state.c to fail
to compile with gcc-9. The code in nfsd4_get_drc_mem() was written with
the assumption that when "max < min",

   clamp(val, min, max)

would return max.  This assumption is not documented as an API promise
and the change caused a compile failure if it could be statically
determined that "max < min".

The relevant code was no longer present upstream when commit 1519fbc8832b
("minmax.h: use BUILD_BUG_ON_MSG() for the lo < hi test in clamp()")
landed there, so there is no upstream change to nfsd4_get_drc_mem() to
backport.

There is no clear case that the existing code in nfsd4_get_drc_mem()
is functioning incorrectly. The goal of this patch is to permit the clean
application of commit 1519fbc8832b ("minmax.h: use BUILD_BUG_ON_MSG() for
the lo < hi test in clamp()"), and any commits that depend on it, to LTS
kernels without affecting the ability to compile those kernels. This is
done by open-coding the __clamp() macro sans the built-in type checking.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220745#c0
Signed-off-by: NeilBrown <neil at brown.name>
Stable-dep-of: 1519fbc8832b ("minmax.h: use BUILD_BUG_ON_MSG() for the lo < hi test in clamp()")
Signed-off-by: Chuck Lever <chuck.lever at oracle.com>
Reviewed_by: David Laight <david.laight.linux at gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 5f4720ac8e67f41020cb39c678e4a3bdc26114fe 6.1.y)
Signed-off-by Satya Jhaveri <satya.jhaveri at canonical.com>
---
 fs/nfsd/nfs4state.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index df982830efc2..1ba5b6369eac 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1822,8 +1822,10 @@ static u32 nfsd4_get_drc_mem(struct nfsd4_channel_attrs *ca, struct nfsd_net *nn
 	 */
 	scale_factor = max_t(unsigned int, 8, nn->nfsd_serv->sv_nrthreads);
 
-	avail = clamp_t(unsigned long, avail, slotsize,
-			total_avail/scale_factor);
+	if (avail > total_avail / scale_factor)
+		avail = total_avail / scale_factor;
+	else if (avail < slotsize)
+		avail = slotsize;
 	num = min_t(int, num, avail / slotsize);
 	num = max_t(int, num, 1);
 	nfsd_drc_mem_used += num * slotsize;
-- 
2.43.0