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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-10-30 08:02:30 +00:00
c7d03a00b5
Make struct pernet_operations::id unsigned.
There are 2 reasons to do so:
1)
This field is really an index into an zero based array and
thus is unsigned entity. Using negative value is out-of-bound
access by definition.
2)
On x86_64 unsigned 32-bit data which are mixed with pointers
via array indexing or offsets added or subtracted to pointers
are preffered to signed 32-bit data.
"int" being used as an array index needs to be sign-extended
to 64-bit before being used.
void f(long *p, int i)
{
g(p[i]);
}
roughly translates to
movsx rsi, esi
mov rdi, [rsi+...]
call g
MOVSX is 3 byte instruction which isn't necessary if the variable is
unsigned because x86_64 is zero extending by default.
Now, there is net_generic() function which, you guessed it right, uses
"int" as an array index:
static inline void *net_generic(const struct net *net, int id)
{
...
ptr = ng->ptr[id - 1];
...
}
And this function is used a lot, so those sign extensions add up.
Patch snipes ~1730 bytes on allyesconfig kernel (without all junk
messing with code generation):
add/remove: 0/0 grow/shrink: 70/598 up/down: 396/-2126 (-1730)
Unfortunately some functions actually grow bigger.
This is a semmingly random artefact of code generation with register
allocator being used differently. gcc decides that some variable
needs to live in new r8+ registers and every access now requires REX
prefix. Or it is shifted into r12, so [r12+0] addressing mode has to be
used which is longer than [r8]
However, overall balance is in negative direction:
add/remove: 0/0 grow/shrink: 70/598 up/down: 396/-2126 (-1730)
function old new delta
nfsd4_lock 3886 3959 +73
tipc_link_build_proto_msg 1096 1140 +44
mac80211_hwsim_new_radio 2776 2808 +32
tipc_mon_rcv 1032 1058 +26
svcauth_gss_legacy_init 1413 1429 +16
tipc_bcbase_select_primary 379 392 +13
nfsd4_exchange_id 1247 1260 +13
nfsd4_setclientid_confirm 782 793 +11
...
put_client_renew_locked 494 480 -14
ip_set_sockfn_get 730 716 -14
geneve_sock_add 829 813 -16
nfsd4_sequence_done 721 703 -18
nlmclnt_lookup_host 708 686 -22
nfsd4_lockt 1085 1063 -22
nfs_get_client 1077 1050 -27
tcf_bpf_init 1106 1076 -30
nfsd4_encode_fattr 5997 5930 -67
Total: Before=154856051, After=154854321, chg -0.00%
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
132 lines
3 KiB
C
132 lines
3 KiB
C
/*
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* Common code for control of lockd and nfsv4 grace periods.
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*
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* Transplanted from lockd code
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*/
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#include <linux/module.h>
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#include <net/net_namespace.h>
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#include <net/netns/generic.h>
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#include <linux/fs.h>
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static unsigned int grace_net_id;
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static DEFINE_SPINLOCK(grace_lock);
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/**
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* locks_start_grace
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* @net: net namespace that this lock manager belongs to
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* @lm: who this grace period is for
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*
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* A grace period is a period during which locks should not be given
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* out. Currently grace periods are only enforced by the two lock
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* managers (lockd and nfsd), using the locks_in_grace() function to
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* check when they are in a grace period.
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*
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* This function is called to start a grace period.
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*/
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void
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locks_start_grace(struct net *net, struct lock_manager *lm)
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{
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struct list_head *grace_list = net_generic(net, grace_net_id);
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spin_lock(&grace_lock);
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list_add(&lm->list, grace_list);
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spin_unlock(&grace_lock);
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}
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EXPORT_SYMBOL_GPL(locks_start_grace);
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/**
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* locks_end_grace
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* @net: net namespace that this lock manager belongs to
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* @lm: who this grace period is for
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*
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* Call this function to state that the given lock manager is ready to
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* resume regular locking. The grace period will not end until all lock
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* managers that called locks_start_grace() also call locks_end_grace().
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* Note that callers count on it being safe to call this more than once,
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* and the second call should be a no-op.
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*/
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void
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locks_end_grace(struct lock_manager *lm)
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{
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spin_lock(&grace_lock);
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list_del_init(&lm->list);
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spin_unlock(&grace_lock);
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}
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EXPORT_SYMBOL_GPL(locks_end_grace);
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/**
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* locks_in_grace
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*
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* Lock managers call this function to determine when it is OK for them
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* to answer ordinary lock requests, and when they should accept only
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* lock reclaims.
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*/
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int
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__state_in_grace(struct net *net, bool open)
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{
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struct list_head *grace_list = net_generic(net, grace_net_id);
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struct lock_manager *lm;
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if (!open)
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return !list_empty(grace_list);
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list_for_each_entry(lm, grace_list, list) {
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if (lm->block_opens)
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return true;
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}
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return false;
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}
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int locks_in_grace(struct net *net)
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{
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return __state_in_grace(net, 0);
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}
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EXPORT_SYMBOL_GPL(locks_in_grace);
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int opens_in_grace(struct net *net)
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{
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return __state_in_grace(net, 1);
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}
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EXPORT_SYMBOL_GPL(opens_in_grace);
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static int __net_init
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grace_init_net(struct net *net)
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{
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struct list_head *grace_list = net_generic(net, grace_net_id);
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INIT_LIST_HEAD(grace_list);
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return 0;
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}
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static void __net_exit
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grace_exit_net(struct net *net)
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{
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struct list_head *grace_list = net_generic(net, grace_net_id);
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BUG_ON(!list_empty(grace_list));
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}
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static struct pernet_operations grace_net_ops = {
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.init = grace_init_net,
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.exit = grace_exit_net,
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.id = &grace_net_id,
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.size = sizeof(struct list_head),
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};
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static int __init
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init_grace(void)
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{
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return register_pernet_subsys(&grace_net_ops);
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}
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static void __exit
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exit_grace(void)
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{
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unregister_pernet_subsys(&grace_net_ops);
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}
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MODULE_AUTHOR("Jeff Layton <jlayton@primarydata.com>");
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MODULE_LICENSE("GPL");
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module_init(init_grace)
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module_exit(exit_grace)
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