Messages in this thread |  | | Subject | Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1 | From | Bernd Edlinger <> | Date | Sat, 4 Apr 2020 07:43:42 +0200 |
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On 4/3/20 6:23 PM, Linus Torvalds wrote: > On Fri, Apr 3, 2020 at 8:09 AM Bernd Edlinger <bernd.edlinger@hotmail.de> wrote: >> >> On 4/2/20 9:04 PM, Linus Torvalds wrote: >>> In fact, then you could drop the >>> >>> mutex_unlock(&tsk->signal->exec_update_mutex); >>> >>> in the error case of exec_mmap(), because now the error handling in >>> free_bprm() would do the cleanup automatically. >>> >> >> The error handling is sometimes called when the exec_update_mutex is >> not taken, in fact even de_thread not called. > > But that's the whole point of the flag. Make the flag be about "do I > hold the mutex", and then the error handling does the right thing > regardless. > >> Can you say how you would suggest that to be done? > > I think the easiest thing to do to explain is to just write the patch. > > This is entirely untested, but see what the difference is? I make the > flag be about exactly where I take the lock, not about some "I have > called exec_mmap". > > Which means that now exec_mmap() doesn't even need to unlock it in the > error case, because the unlocking will happen properly in the > bprm_exit regardless. > > This makes that unconditional unlocking logic much more obvious. > > That said, Eric says he can make it all properly static so that it > doesn't need that kind of dynamic "if (x) unlock()" logic at all, > which is much better. > > So this patch is not for consumption, it's purely for "look, something > like this" >
Just one suggestion, in general It would feel pretty much okay if you like to improve the naming, and the consistency in any of my patches.
> @@ -1067,7 +1069,6 @@ static int exec_mmap(struct mm_struct *mm) > down_read(&old_mm->mmap_sem); > if (unlikely(old_mm->core_state)) { > up_read(&old_mm->mmap_sem); > - mutex_unlock(&tsk->signal->exec_update_mutex);
I was trying to replicate the behavior of prepare_bprm_creds which also unlocks the mutex in the error case, therefore it felt okay to unlock the mutex here, but it will work either way.
I should further note, that the mutex would be locked if this error exit is taken, and unlocked if this error happens:
ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); if (ret) return ret;
so at least the function comment I introduced above should be updated: * Maps the mm_struct mm into the current task struct. * On success, this function returns with the mutex * exec_update_mutex locked.
> put_binfmt(fmt); > - if (retval < 0 && bprm->called_exec_mmap) { > + if (retval < 0 && !bprm->mm) {
Using bprm->mm like this feels like a hack to me. It works here, but nowhere else. Therefore I changed this line.
Using !bprm->mm in the error handling code made Eric's patch fail.
Thanks Bernd.
> Linus >
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