On 1/28/15 00:11, Michael Tokarev wrote: > 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". >
OK, thanks, I shall notice about them, next time. > 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. > OK, it sounds good to me. > 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. > For me, when process paired functions, need consider a little more. - Are there any recurse code between lock/unlock? - After lock, do any code call unlock indirectly? Or before unlock(), do any code call lock() indirectly? - Between 2 unlocks (or 2 locks), does any code call lock (or unlock) indirectly? In our case, queue_signal() may call lock indirectly between 2 unlocks, So for me, the patch is necessary to mention about queue_signal() in commit comments. >> 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". > OK. >> 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? > For me, I still suggest to give some descriptions for queue_signal(). Thanks. -- Chen Gang Open, share, and attitude like air, water, and life which God blessed
