Since commit de766e570413 ("nfsd: give out fewer session slots as
limit approaches") nfsd4_get_drc_mem() ensures 'avail' is always at
least 'slotsize', so the return value 'num' is always at least 1.
This means that:
1/ nfsd_drc_mem_used could exceed nfsd_drc_max_mem, which becomes
a problem when we later perform an unsigned subtraction of
the larger from the smaller to calculate 'total_avail'.
2/ Check the return value of nfsd4_get_drc_mem() against
zero is pointless - the error code (which isn't actually correct
according to RFC-5661) is never returned.
So avoid the integer overflow, and discard the check.
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
fs/nfsd/nfs4state.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 7857942c5ca6..8c09ac49fff2 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1570,11 +1570,21 @@ static u32 nfsd4_get_drc_mem(struct nfsd4_channel_attrs *ca)
unsigned long avail, total_avail;
spin_lock(&nfsd_drc_lock);
- total_avail = nfsd_drc_max_mem - nfsd_drc_mem_used;
+ if (nfsd_drc_max_mem > nfsd_drc_mem_used)
+ total_avail = nfsd_drc_max_mem - nfsd_drc_mem_used;
+ else
+ /* We have handed out more space than we chose in
+ * set_max_drc() to allow. That isn't really a
+ * problem as long as that doesn't make us thing we
+ * have lots more due to integer overflow.
+ */
+ total_avail = 0;
avail = min((unsigned long)NFSD_MAX_MEM_PER_SESSION, total_avail);
/*
* Never use more than a third of the remaining memory,
* unless it's the only way to give this client a slot:
+ * Note that we always return at least 1 here, even if
+ * we have exceeded nfsd_drc_max_mem.
*/
avail = clamp_t(unsigned long, avail, slotsize, total_avail/3);
num = min_t(int, num, avail / slotsize);
@@ -3169,10 +3179,10 @@ static __be32 check_forechannel_attrs(struct nfsd4_channel_attrs *ca, struct nfs
* performance. When short on memory we therefore prefer to
* decrease number of slots instead of their size. Clients that
* request larger slots than they need will get poor results:
+ * Note that we always allow at least one slot, because our
+ * accounting is soft and provides no guarantees either way.
*/
ca->maxreqs = nfsd4_get_drc_mem(ca);
- if (!ca->maxreqs)
- return nfserr_jukebox;
return nfs_ok;
}
--
2.23.0
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