Commit 23918b03 authored by Trond Myklebust's avatar Trond Myklebust Committed by Linus Torvalds
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SUNRPC: Fix a performance regression in the RPC authentication code

Fix a regression reported by Max Kellermann whereby kernel profiling
showed that his clients were spending 45% of their time in

It turns out that although his processes had identical uid/gid/groups,
generic_match() was failing to detect this, because the task->group_info
pointers were not shared. This again lead to the creation of a huge number
of identical credentials at the RPC layer.

The regression is fixed by comparing the contents of task->group_info
if the actual pointers are not identical.
Signed-off-by: default avatarTrond Myklebust <>
Signed-off-by: default avatarLinus Torvalds <>
parent 0cb39aa0
......@@ -133,13 +133,29 @@ static int
generic_match(struct auth_cred *acred, struct rpc_cred *cred, int flags)
struct generic_cred *gcred = container_of(cred, struct generic_cred, gc_base);
int i;
if (gcred->acred.uid != acred->uid ||
gcred->acred.gid != acred->gid ||
gcred->acred.group_info != acred->group_info ||
gcred->acred.machine_cred != acred->machine_cred)
return 0;
goto out_nomatch;
/* Optimisation in the case where pointers are identical... */
if (gcred->acred.group_info == acred->group_info)
goto out_match;
/* Slow path... */
if (gcred->acred.group_info->ngroups != acred->group_info->ngroups)
goto out_nomatch;
for (i = 0; i < gcred->acred.group_info->ngroups; i++) {
if (GROUP_AT(gcred->acred.group_info, i) !=
GROUP_AT(acred->group_info, i))
goto out_nomatch;
return 1;
return 0;
void __init rpc_init_generic_auth(void)
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