Date: Tue, 12 Sep 2000 10:13:48 +0100 (BST) From: Doug Rabson <dfr@nlsystems.com> To: John Baldwin <jhb@pike.osd.bsdi.com> Cc: dfr@FreeBSD.org, alpha@FreeBSD.org Subject: Re: Bug in spinlocks? Message-ID: <Pine.BSF.4.21.0009121010170.86297-100000@salmon.nlsystems.com> In-Reply-To: <200009112037.NAA61735@pike.osd.bsdi.com>
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On Mon, 11 Sep 2000, John Baldwin wrote:
> Hmm, is there any reason why we aren't disabling interrupts on the alpha
> when we obtain spinlocks? In the i386 code we use the following macro:
>
> /* Get a spin lock, handle recursion inline (as the less common case) */
> #define _getlock_spin_block(mp, tid, type) do { \
> u_int _mtx_fl = read_eflags(); \
> disable_intr(); \
> if (atomic_cmpset_int(&(mp)->mtx_lock, MTX_UNOWNED, (tid)) == 0) \
> mtx_enter_hard(mp, (type) & MTX_HARDOPTS, _mtx_fl); \
> else \
> (mp)->mtx_savefl = _mtx_fl; \
> } while (0)
>
> on the alpha it is almost the same:
>
> /*
> * Get a spin lock, handle recusion inline (as the less common case)
> */
>
> #define _getlock_spin_block(mp, tid, type) do { \
> u_int _ipl = alpha_pal_rdps() & ALPHA_PSL_IPL_MASK; \
> if (atomic_cmpset_64(&(mp)->mtx_lock, MTX_UNOWNED, (tid)) == 0) \
> mtx_enter_hard(mp, (type) & MTX_HARDOPTS, _ipl); \
> else { \
> alpha_mb(); \
> (mp)->mtx_saveipl = _ipl; \
> } \
> } while (0)
>
> Note that in the alpha we are just saving and restoring the ipl, but we
> aren't actually changing it to disable interrupts.
Looks like a major brain failure on my part. Try these (untested) changes:
Index: mutex.h
===================================================================
RCS file: /home/ncvs/src/sys/alpha/include/mutex.h,v
retrieving revision 1.5
diff -u -r1.5 mutex.h
--- mutex.h 2000/09/09 23:18:47 1.5
+++ mutex.h 2000/09/12 09:13:25
@@ -223,9 +223,9 @@
extern char STR_IEN[];
extern char STR_IDIS[];
#endif /* MTX_STRS */
-#define ASS_IEN MPASS2((alpha_pal_rdps & ALPHA_PSL_IPL_MASK) \
+#define ASS_IEN MPASS2((alpha_pal_rdps() & ALPHA_PSL_IPL_MASK) \
== ALPHA_PSL_IPL_HIGH, STR_IEN)
-#define ASS_IDIS MPASS2((alpha_pal_rdps & ALPHA_PSL_IPL_MASK) \
+#define ASS_IDIS MPASS2((alpha_pal_rdps() & ALPHA_PSL_IPL_MASK) \
!= ALPHA_PSL_IPL_HIGH, STR_IDIS)
#endif /* INVARIANTS */
@@ -326,7 +326,7 @@
*/
#define _getlock_spin_block(mp, tid, type) do { \
- u_int _ipl = alpha_pal_rdps() & ALPHA_PSL_IPL_MASK; \
+ u_int _ipl = alpha_pal_swpipl(ALPHA_PSL_IPL_HIGH); \
if (atomic_cmpset_64(&(mp)->mtx_lock, MTX_UNOWNED, (tid)) == 0) \
mtx_enter_hard(mp, (type) & MTX_HARDOPTS, _ipl); \
else { \
@@ -544,8 +544,8 @@
* Simple assembly macros to get and release non-recursive spin locks
*/
#define MTX_ENTER(lck) \
- call_pal PAL_OSF1_rdps; \
- and v0, ALPHA_PSL_IPL_MASK, v0; \
+ ldiq a0, ALPHA_PSL_IPL_HIGH; \
+ call_pal PAL_OSF1_swpipl; \
1: ldq_l a0, lck+MTX_LOCK; \
cmpeq a0, MTX_UNOWNED, a1; \
beq a1, 1b; \
@@ -553,9 +553,7 @@
stq_c a0, lck+MTX_LOCK; \
beq a0, 1b; \
mb; \
- stl v0, lck+MTX_SAVEIPL; \
- ldq a0, ALPHA_PSL_IPL_HIGH; \
- call_pal PSL_OSF1_swpipl
+ stl v0, lck+MTX_SAVEIPL
#define MTX_EXIT(lck) \
mb; \
--
Doug Rabson Mail: dfr@nlsystems.com
Nonlinear Systems Ltd. Phone: +44 20 8348 3944
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