From patchwork Mon Mar 1 22:33:23 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: Regression: segfault on ARM host Date: Mon, 01 Mar 2010 12:33:23 -0000 From: Paolo Bonzini X-Patchwork-Id: 46615 Message-Id: <4B8C40B3.6030008@redhat.com> To: Aurelien Jarno Cc: qemu-devel On 03/01/2010 10:33 PM, Aurelien Jarno wrote: > While trying to implement setcond on TCG ARM, I have discovered it does > not work anymore. I have bisected this regression to: > > commit 6113d6d3169393c323ac4c82d756a850145a5e7a > Author: Paolo Bonzini > Date: Fri Jan 15 09:42:09 2010 +0100 > > change while to if > > The while loop will be executed exactly 0 or 1 times, depending on > env->exit_request. > > Signed-off-by: Paolo Bonzini > Signed-off-by: Anthony Liguori > > The assertion is actually triggered. When the next patch removing the > assertion is also applied it segfaults instead. Looks like a race. The only piece of logic that is changed by that commit is reverted in the attached patch, can you try it? If it passes, I can resubmit with S-o-b. If it doesn't pass, I wonder whether the while loop was there to trick the compiler into not optimizing something. Seems a bit too clever though. Paolo diff --git a/cpu-exec.c b/cpu-exec.c index 5d6dd51..61b1c59 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -602,9 +602,15 @@ int cpu_exec(CPUState *env1) /* cpu_interrupt might be called while translating the TB, but before it is linked into a potentially infinite loop and becomes env->current_tb. Avoid - starting execution if there is a pending interrupt. */ - if (!unlikely (env->exit_request)) { - env->current_tb = tb; + starting execution if there is a pending interrupt. + Doing it this way is necessary to avoid races with + cpu_unlink_tb (called by cpu_exit). */ + env->current_tb = tb; + if (unlikely (env->exit_request)) { + env->current_tb = NULL; + } + + if (likely (env->current_tb)) { tc_ptr = tb->tc_ptr; /* execute the generated code */ #if defined(__sparc__) && !defined(CONFIG_SOLARIS)