Add a memory barrier after taking a reference on the vnode holdcnt in _vhold
This is needed to avoid a race between the VNASSERT() below, and another thread updating the VI_FREE flag, on weakly-ordered architectures. On a 72-thread POWER9, without this barrier a 'make -j72 buildworld' would panic on the assert regularly. It may be possible to use a weaker barrier, and I'll investigate that once all stability issues are worked out on POWER9.
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=334708
@ -2807,6 +2807,9 @@ _vhold(struct vnode *vp, bool locked)
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CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
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if (!locked) {
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if (refcount_acquire_if_not_zero(&vp->v_holdcnt)) {
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#if !defined(__amd64__) && !defined(__i386__)
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mb();
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#endif
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VNASSERT((vp->v_iflag & VI_FREE) == 0, vp,
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("_vhold: vnode with holdcnt is free"));
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return;
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