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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.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Sergey Fedorov 2016-04-20 23:15:09 +03:00 committed by Richard Henderson
parent 901bc3deb4
commit 9962c478b1
1 changed files with 16 additions and 13 deletions
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29
include/exec/exec-all.h
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@ -372,20 +372,23 @@ 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,