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[Qemu-devel] [PATCH v2 5/8] tcg: Clarify thread safety check in tb_add_j
From: |
sergey . fedorov |
Subject: |
[Qemu-devel] [PATCH v2 5/8] tcg: Clarify thread safety check in tb_add_jump() |
Date: |
Fri, 25 Mar 2016 00:56:44 +0300 |
From: Sergey Fedorov <address@hidden>
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 <address@hidden>
Signed-off-by: Sergey Fedorov <address@hidden>
---
Notes:
Changes in v2:
* Typo fixed in the commit title
* Complete rewrite of the commit body and the patch based on Paolo's
comments
include/exec/exec-all.h | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index db5c658919ad..45142ebab9e2 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -391,16 +391,19 @@ 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]) {
- /* 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;
- assert(((uintptr_t)tb & 3) == 0);
- 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;
}
+
+ /* 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;
+ assert(((uintptr_t)tb & 3) == 0);
+ tb_next->jmp_list_first = (uintptr_t)tb | n;
}
/* GETRA is the true target of the return instruction that we'll execute,
--
2.7.3
- [Qemu-devel] [PATCH v2 0/8] tcg: Direct block chaining clean-up, sergey . fedorov, 2016/03/24
- [Qemu-devel] [PATCH v2 2/8] tcg: Use uintptr_t type for jmp_list_{next|first} fields of TB, sergey . fedorov, 2016/03/24
- [Qemu-devel] [PATCH v2 3/8] tcg: Rearrange tb_link_page() to avoid forward declaration, sergey . fedorov, 2016/03/24
- [Qemu-devel] [PATCH v2 4/8] tcg: Init TB's direct jumps before making it visible, sergey . fedorov, 2016/03/24
- [Qemu-devel] [PATCH v2 1/8] tcg: Clean up direct block chaining data fields, sergey . fedorov, 2016/03/24
- [Qemu-devel] [PATCH v2 5/8] tcg: Clarify thread safety check in tb_add_jump(),
sergey . fedorov <=
- [Qemu-devel] [PATCH v2 6/8] tcg: Rename tb_jmp_remove() to tb_remove_from_jmp_list(), sergey . fedorov, 2016/03/24
- [Qemu-devel] [PATCH v2 7/8] tcg: Extract removing of jumps to TB from tb_phys_invalidate(), sergey . fedorov, 2016/03/24
- [Qemu-devel] [PATCH v2 8/8] tcg: Clean up tb_jmp_unlink(), sergey . fedorov, 2016/03/24