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vfs: prevent numvnodes and freevnodes re-reads when appropriate

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Otherwise in code like this:
if (numvnodes > desiredvnodes)
	vnlru_free_locked(numvnodes - desiredvnodes, NULL);

numvnodes can drop below desiredvnodes prior to the call and if the
compiler generated another read the subtraction would get a negative
value.
This commit is contained in:
Mateusz Guzik 2020-01-07 04:34:03 +00:00
parent 9a67c570a9
commit cc2b586d69
1 changed files with 23 additions and 12 deletions
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35
sys/kern/vfs_subr.c
View File

@ -1211,16 +1211,19 @@ vnlru_free(int count, struct vfsops *mnt_op)
static int
vspace(void)
{
u_long rnumvnodes, rfreevnodes;
int space;
gapvnodes = imax(desiredvnodes - wantfreevnodes, 100);
vhiwat = gapvnodes / 11; /* 9% -- just under the 10% in vlrureclaim() */
vlowat = vhiwat / 2;
if (numvnodes > desiredvnodes)
rnumvnodes = atomic_load_long(&numvnodes);
rfreevnodes = atomic_load_long(&freevnodes);
if (rnumvnodes > desiredvnodes)
return (0);
space = desiredvnodes - numvnodes;
space = desiredvnodes - rnumvnodes;
if (freevnodes > wantfreevnodes)
space += freevnodes - wantfreevnodes;
space += rfreevnodes - wantfreevnodes;
return (space);
}
@ -1292,6 +1295,7 @@ static int vnlruproc_sig;
static void
vnlru_proc(void)
{
u_long rnumvnodes, rfreevnodes;
struct mount *mp, *nmp;
unsigned long onumvnodes;
int done, force, trigger, usevnodes, vsp;
@ -1304,13 +1308,14 @@ vnlru_proc(void)
for (;;) {
kproc_suspend_check(vnlruproc);
mtx_lock(&vnode_free_list_mtx);
rnumvnodes = atomic_load_long(&numvnodes);
/*
* If numvnodes is too large (due to desiredvnodes being
* adjusted using its sysctl, or emergency growth), first
* try to reduce it by discarding from the free list.
*/
if (numvnodes > desiredvnodes)
vnlru_free_locked(numvnodes - desiredvnodes, NULL);
if (rnumvnodes > desiredvnodes)
vnlru_free_locked(rnumvnodes - desiredvnodes, NULL);
/*
* Sleep if the vnode cache is in a good state. This is
* when it is not over-full and has space for about a 4%
@ -1332,7 +1337,10 @@ vnlru_proc(void)
}
mtx_unlock(&vnode_free_list_mtx);
done = 0;
onumvnodes = numvnodes;
rnumvnodes = atomic_load_long(&numvnodes);
rfreevnodes = atomic_load_long(&freevnodes);
onumvnodes = rnumvnodes;
/*
* Calculate parameters for recycling. These are the same
* throughout the loop to give some semblance of fairness.
@ -1340,10 +1348,10 @@ vnlru_proc(void)
* of resident pages. We aren't trying to free memory; we
* are trying to recycle or at least free vnodes.
*/
if (numvnodes <= desiredvnodes)
usevnodes = numvnodes - freevnodes;
if (rnumvnodes <= desiredvnodes)
usevnodes = rnumvnodes - rfreevnodes;
else
usevnodes = numvnodes;
usevnodes = rnumvnodes;
if (usevnodes <= 0)
usevnodes = 1;
/*
@ -1516,14 +1524,17 @@ getnewvnode_wait(int suspended)
void
getnewvnode_reserve(u_int count)
{
u_long rnumvnodes, rfreevnodes;
struct thread *td;
/* Pre-adjust like the pre-adjust in getnewvnode(), with any count. */
/* XXX no longer so quick, but this part is not racy. */
mtx_lock(&vnode_free_list_mtx);
if (numvnodes + count > desiredvnodes && freevnodes > wantfreevnodes)
vnlru_free_locked(ulmin(numvnodes + count - desiredvnodes,
freevnodes - wantfreevnodes), NULL);
rnumvnodes = atomic_load_long(&numvnodes);
rfreevnodes = atomic_load_long(&freevnodes);
if (rnumvnodes + count > desiredvnodes && rfreevnodes > wantfreevnodes)
vnlru_free_locked(ulmin(rnumvnodes + count - desiredvnodes,
rfreevnodes - wantfreevnodes), NULL);
mtx_unlock(&vnode_free_list_mtx);
td = curthread;