xtensa: add missing exclusive access state management

The result of the s32ex opcode is recorded in the ATOMCTL special
register and must be retrieved with the getex opcode. Context switch
between s32ex and getex may trash the ATOMCTL register and result in
duplicate update or missing update of the atomic variable.
Add atomctl8 field to the struct thread_info and use getex to swap
ATOMCTL bit 8 as a part of context switch.
Clear exclusive access monitor on kernel entry.

Cc: stable@vger.kernel.org
Fixes: f7c34874f04a ("xtensa: add exclusive atomics support")
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

diff --git a/arch/xtensa/include/asm/thread_info.h b/arch/xtensa/include/asm/thread_info.h
index 8918f0f..6acbbe0 100644 (file)
--- a/arch/xtensa/include/asm/thread_info.h
+++ b/arch/xtensa/include/asm/thread_info.h
@@ -55,6 +55,10 @@ struct thread_info {
        mm_segment_t            addr_limit;     /* thread address space */
 
        unsigned long           cpenable;
+#if XCHAL_HAVE_EXCLUSIVE
+       /* result of the most recent exclusive store */
+       unsigned long           atomctl8;
+#endif
 
        /* Allocate storage for extra user states and coprocessor states. */
 #if XTENSA_HAVE_COPROCESSORS

diff --git a/arch/xtensa/kernel/asm-offsets.c b/arch/xtensa/kernel/asm-offsets.c
index 33a257b..dc5c83c 100644 (file)
--- a/arch/xtensa/kernel/asm-offsets.c
+++ b/arch/xtensa/kernel/asm-offsets.c
@@ -93,6 +93,9 @@ int main(void)
        DEFINE(THREAD_RA, offsetof (struct task_struct, thread.ra));
        DEFINE(THREAD_SP, offsetof (struct task_struct, thread.sp));
        DEFINE(THREAD_CPENABLE, offsetof (struct thread_info, cpenable));
+#if XCHAL_HAVE_EXCLUSIVE
+       DEFINE(THREAD_ATOMCTL8, offsetof (struct thread_info, atomctl8));
+#endif
 #if XTENSA_HAVE_COPROCESSORS
        DEFINE(THREAD_XTREGS_CP0, offsetof(struct thread_info, xtregs_cp.cp0));
        DEFINE(THREAD_XTREGS_CP1, offsetof(struct thread_info, xtregs_cp.cp1));

diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 98515c2..703cf62 100644 (file)
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -374,6 +374,11 @@ common_exception:
        s32i    a2, a1, PT_LCOUNT
 #endif
 
+#if XCHAL_HAVE_EXCLUSIVE
+       /* Clear exclusive access monitor set by interrupted code */
+       clrex
+#endif
+
        /* It is now save to restore the EXC_TABLE_FIXUP variable. */
 
        rsr     a2, exccause
@@ -2020,6 +2025,12 @@ ENTRY(_switch_to)
        s32i    a3, a4, THREAD_CPENABLE
 #endif
 
+#if XCHAL_HAVE_EXCLUSIVE
+       l32i    a3, a5, THREAD_ATOMCTL8
+       getex   a3
+       s32i    a3, a4, THREAD_ATOMCTL8
+#endif
+
        /* Flush register file. */
 
        spill_registers_kernel