25.01.2015 14:03, Chen Gang S wrote: > start/end_exclusive() need be pairs, except the start_exclusive() in
"need TO be pairs", or "should be pairs" or "should be called in pairs". > stop_all_tasks() which is only used by force_sig(), which will be abort. "which will abort" or "which will call abort()" or "which calls abort()". > So at present, start_exclusive() in stop_all_task() need not be paired. > > queue_signal() may call force_sig(), or return after kill pid (or queue > signal). "or return after killing pid (or queuing signal)". > If could return from queue_signal(), stop_all_task() would not > be called in time, "if queue_signal() returns > the next end_exclusive() would be issue. "would be AN issue". But actually we're interested to know answer to a slightly different question: whenever queue_signal() returns or not (it doesn't return in force_sig case). So whole this part becomes something like: queue_signal() may either call force_sig() and die, or return. In the latter case, stop_all_task() would not be called in time, so next end_exclusive() will be an issue. And even more, when you look at this function (arm_kernel_cmpxchg64_helper), you'll notice it has two calls to end_exclusive() in sigsegv case, without a call to start_exclusive(). _That_ is, I think, the key point here -- the rest of the information here is not really very relevant, because the actual problem is this double call to end_exclusive() which should be removed. It is not really that interesting to know that it's not _necessary_ to call end_exclusive() in some cases which leads to abort(), because this is not one of them anyway (since queue_signal() might return just fine), and because while it is not necessary, it is not an error either. With all this extra info, thie commit message becomes just too confusing. > So in arm_kernel_cmpxchg64_helper() for ARM, need remove end_exclusive() > after queue_signal(). "need TO remove", and again the missing subject. "We need to remove", or "we should remove", or, yet another variant, "extra end_exclusive() call should be removed". > The related commit: "97cc756 linux-user: Implement > new ARM 64 bit cmpxchg kernel helper". So, how about this (the subject is fine): start/end_exclusive() should be paired to each other. However, in arm_kernel_cmpxchg64_helper() function, end_exclusive() is called twice in a row. Remove the second, redundrand, call. Commit which introduced this problem is"97cc756 linux-user: Implement new ARM 64 bit cmpxchg kernel helper". ? Did I understand the problem correctly? Thanks, /mjt > Signed-off-by: Chen Gang <gang.chen.5...@gmail.com> > --- > linux-user/main.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/linux-user/main.c b/linux-user/main.c > index 8c70be4..2d52c1f 100644 > --- a/linux-user/main.c > +++ b/linux-user/main.c > @@ -523,8 +523,6 @@ segv: > info.si_code = TARGET_SEGV_MAPERR; > info._sifields._sigfault._addr = env->exception.vaddress; > queue_signal(env, info.si_signo, &info); > - > - end_exclusive(); > } > > /* Handle a jump to the kernel code page. */ >
