tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
1
fork

Configure Feed

Select the types of activity you want to include in your feed.

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
rpcauth_lookup_credcache.

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: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

authored by

Trond Myklebust and committed by
Linus Torvalds 23918b03 0cb39aa0

+18 -2
+18 -2
net/sunrpc/auth_generic.c
··· 133 133 generic_match(struct auth_cred *acred, struct rpc_cred *cred, int flags) 134 134 { 135 135 struct generic_cred *gcred = container_of(cred, struct generic_cred, gc_base); 136 + int i; 136 137 137 138 if (gcred->acred.uid != acred->uid || 138 139 gcred->acred.gid != acred->gid || 139 - gcred->acred.group_info != acred->group_info || 140 140 gcred->acred.machine_cred != acred->machine_cred) 141 - return 0; 141 + goto out_nomatch; 142 + 143 + /* Optimisation in the case where pointers are identical... */ 144 + if (gcred->acred.group_info == acred->group_info) 145 + goto out_match; 146 + 147 + /* Slow path... */ 148 + if (gcred->acred.group_info->ngroups != acred->group_info->ngroups) 149 + goto out_nomatch; 150 + for (i = 0; i < gcred->acred.group_info->ngroups; i++) { 151 + if (GROUP_AT(gcred->acred.group_info, i) != 152 + GROUP_AT(acred->group_info, i)) 153 + goto out_nomatch; 154 + } 155 + out_match: 142 156 return 1; 157 + out_nomatch: 158 + return 0; 143 159 } 144 160 145 161 void __init rpc_init_generic_auth(void)