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tcg: Clarify thread safety check in tb_add_jump()

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The check is to make sure that another thread hasn't already done the
same while we were outside of tb_lock. Mention this in a comment.

Backports commit 9962c478b153a18fe88a6509fe58cd178aff8abc from qemu
This commit is contained in:
Sergey Fedorov 2018-02-23 21:32:44 -05:00 committed by Lioncash
parent e93f68a755
commit d60af028c5
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GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 16 additions and 13 deletions
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29
qemu/include/exec/exec-all.h
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@ -366,20 +366,23 @@ static inline void tb_set_jmp_target(TranslationBlock *tb,
static inline void tb_add_jump(TranslationBlock *tb, int n,
TranslationBlock *tb_next)
{
/* NOTE: this test is only needed for thread safety */
if (!tb->jmp_list_next[n]) {
qemu_log_mask_and_addr(CPU_LOG_EXEC, tb->pc,
"Linking TBs %p [" TARGET_FMT_lx
"] index %d -> %p [" TARGET_FMT_lx "]\n",
tb->tc_ptr, tb->pc, n,
tb_next->tc_ptr, tb_next->pc);
/* patch the native jump address */
tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc_ptr);
/* add in TB jmp circular list */
tb->jmp_list_next[n] = tb_next->jmp_list_first;
tb_next->jmp_list_first = (uintptr_t)tb | n;
if (tb->jmp_list_next[n]) {
/* Another thread has already done this while we were
* outside of the lock; nothing to do in this case */
return;
}
qemu_log_mask_and_addr(CPU_LOG_EXEC, tb->pc,
"Linking TBs %p [" TARGET_FMT_lx
"] index %d -> %p [" TARGET_FMT_lx "]\n",
tb->tc_ptr, tb->pc, n,
tb_next->tc_ptr, tb_next->pc);
/* patch the native jump address */
tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc_ptr);
/* add in TB jmp circular list */
tb->jmp_list_next[n] = tb_next->jmp_list_first;
tb_next->jmp_list_first = (uintptr_t)tb | n;
}
/* GETRA is the true target of the return instruction that we'll execute,