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 07:48:58 +0200 |
| |
On 4/4/20 7:43 AM, Bernd Edlinger wrote: > > > 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. >
That does probably work better it the boolean is named after_the_point_of_no_return or something....
> > Thanks > Bernd. > > >> Linus >>
|  |