From: NeilBrown neil@brown.name
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@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@oracle.com --- fs/nfsd/nfs4state.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
Changes since Neil's post: * Editorial changes to the commit message * Attempt to address David's review comments * Applied to linux-6.12.y, passed NFSD upstream CI suite
This patch is intended to be applied to linux-6.12.y, and should apply cleanly to other LTS kernels since nfsd4_get_drc_mem hasn't changed since v5.4.
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index 7b0fabf8c657..41545933dd18 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -1983,8 +1983,10 @@ 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;