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translate-all: exit from tb_phys_invalidate if qht_remove fails

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Two or more threads might race while invalidating the same TB. We currently
do not check for this at all despite taking tb_lock, which means we would
wrongly invalidate the same TB more than once. This bug has actually been
hit by users: I recently saw a report on IRC, although I have yet to see
the corresponding test case.

Fix this by using qht_remove as the synchronization point; if it fails,
that means the TB has already been invalidated, and therefore there
is nothing left to do in tb_phys_invalidate.

Note that this solution works now that we still have tb_lock, and will
continue working once we remove tb_lock.

Backports commit cc689485ee3e9dca05765326ee8fd619a6ec48f0 from qemu
This commit is contained in:
Emilio G. Cota 2018-03-15 15:50:36 -04:00 committed by Lioncash
parent cd538f0b7e
commit fc30b3d5cf
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GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 3 additions and 1 deletions
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4
qemu/accel/tcg/translate-all.c
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@ -1114,7 +1114,9 @@ void tb_phys_invalidate(struct uc_struct *uc,
phys_pc = tb->page_addr[0] + (tb->pc & ~TARGET_PAGE_MASK);
h = tb_hash_func(phys_pc, tb->pc, tb->flags, tb->cflags & CF_HASH_MASK,
tb->trace_vcpu_dstate);
qht_remove(&uc->tb_ctx.htable, tb, h);
if (!qht_remove(&uc->tb_ctx.htable, tb, h)) {
return;
}
/* remove the TB from the page list */
if (tb->page_addr[0] != page_addr) {