commit 378df4b23753a11be650af7664ca76bc75cb9f01
author Peter Maydell <peter.maydell@linaro.org> Fri Feb 22 18:10:03 2013 +0000
committer Blue Swirl <blauwirbel@gmail.com> Sun Mar 03 14:28:47 2013 +0000
tree cedcd8fd2c8b23401ca4275ce65388e745cbcb37
parent 77211379d73ea0c89c0b5bb6eee74b17cb06f9a8

Handle CPU interrupts by inline checking of a flag

Fix some of the nasty TCG race conditions and crashes by implementing
cpu_exit() as setting a flag which is checked at the start of each TB.
This avoids crashes if a thread or signal handler calls cpu_exit()
while the execution thread is itself modifying the TB graph (which
may happen in system emulation mode as well as in linux-user mode
with a multithreaded guest binary).

This fixes the crashes seen in LP:668799; however there are another
class of crashes described in LP:1098729 which stem from the fact
that in linux-user with a multithreaded guest all threads will
use and modify the same global TCG date structures (including the
generated code buffer) without any kind of locking. This means that
multithreaded guest binaries are still in the "unsupported"
category.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

cpu-exec.c

diff --git a/cpu-exec.c b/cpu-exec.c
index f9ea080..9092145 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -64,6 +64,12 @@
         TranslationBlock *tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
         cpu_pc_from_tb(env, tb);
     }
+    if ((next_tb & TB_EXIT_MASK) == TB_EXIT_REQUESTED) {
+        /* We were asked to stop executing TBs (probably a pending
+         * interrupt. We've now stopped, so clear the flag.
+         */
+        cpu->tcg_exit_req = 0;
+    }
     return next_tb;
 }
 
@@ -608,7 +614,20 @@
                     tc_ptr = tb->tc_ptr;
                     /* execute the generated code */
                     next_tb = cpu_tb_exec(cpu, tc_ptr);
-                    if ((next_tb & TB_EXIT_MASK) == TB_EXIT_ICOUNT_EXPIRED) {
+                    switch (next_tb & TB_EXIT_MASK) {
+                    case TB_EXIT_REQUESTED:
+                        /* Something asked us to stop executing
+                         * chained TBs; just continue round the main
+                         * loop. Whatever requested the exit will also
+                         * have set something else (eg exit_request or
+                         * interrupt_request) which we will handle
+                         * next time around the loop.
+                         */
+                        tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
+                        next_tb = 0;
+                        break;
+                    case TB_EXIT_ICOUNT_EXPIRED:
+                    {
                         /* Instruction counter expired.  */
                         int insns_left;
                         tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
@@ -632,6 +651,10 @@
                             next_tb = 0;
                             cpu_loop_exit(env);
                         }
+                        break;
+                    }
+                    default:
+                        break;
                     }
                 }
                 cpu->current_tb = NULL;