| Message ID | 20211011133245.1703103-3-brauner@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Introduce simple pidfd to task helper | expand |
On 11.10.21 15:32, Christian Brauner wrote: > From: Christian Brauner <christian.brauner@ubuntu.com> > > Instead of duplicating the same code in two places use the newly added > pidfd_get_task() helper. This fixes an (unimportant for now) bug where > PIDTYPE_PID is used whereas PIDTYPE_TGID should have been used. What would have been the effect of the BUG? Is it worth Fixes: or better even separating out the fix? > > Link: https://lore.kernel.org/r/20211004125050.1153693-3-christian.brauner@ubuntu.com > Cc: Vlastimil Babka <vbabka@suse.cz> > Cc: Suren Baghdasaryan <surenb@google.com> > Cc: Matthew Bobrowski <repnop@google.com> > Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com> > Cc: David Hildenbrand <david@redhat.com> > Cc: Jan Kara <jack@suse.cz> > Cc: Minchan Kim <minchan@kernel.org> > Reviewed-by: Matthew Bobrowski <repnop@google.com> > Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> > --- > /* v2 */ > unchanged Acked-by: David Hildenbrand <david@redhat.com>
On Tue, Oct 12, 2021 at 04:13:31PM +0200, David Hildenbrand wrote: > On 11.10.21 15:32, Christian Brauner wrote: > > From: Christian Brauner <christian.brauner@ubuntu.com> > > > > Instead of duplicating the same code in two places use the newly added > > pidfd_get_task() helper. This fixes an (unimportant for now) bug where > > PIDTYPE_PID is used whereas PIDTYPE_TGID should have been used. > > What would have been the effect of the BUG? Is it worth Fixes: or better Right now, there's no issue. I hope my "unimportant for now" gets that across. Retrieving it via PIDTYPE_PID or PIDTYPE_TGID doesn't matter right now because at pidfd creation time we ensure that: - the pid used with pidfd_open() - the task created via clone{3}()'s CLONE_PIDFD are used as PIDTYPE_TGID, i.e. the struct pid the pidfd references is used as PIDTYPE_TGID, i.e. is a thread-group leader. The concern is for the future were we may want to enable pidfds to refer to individual threads. Once that happens the passed in pidfd to e.g. process_mrelease() or process_madvise() can refer to a struct pid that is only used as PIDTYPE_PID and not as PIDTYPE_TGID, i.e. it might be a pidfd refering to a non-threadgroup leader. Once that happens we want to make sure that all users of pidfds are ok working with non-threadgroup leaders. If we have on central helper that becomes a relatively simple exercise in grepping and we're sure that all current callers use PIDTYPE_TGID as they're using the helper. If we let places use PIDTYPE_PID or PIDTYPE_TGID interchangeably this becomes a more arduous task. So in a sense it's a bug-in-the-making. It's arguably fixes the addition of process_mrelease() since I mentioned this pretty early on and requested the addition of a helper as part of the patchset. I think it just got lost in the reviews though. > even separating out the fix? > > > > > Link: https://lore.kernel.org/r/20211004125050.1153693-3-christian.brauner@ubuntu.com > > Cc: Vlastimil Babka <vbabka@suse.cz> > > Cc: Suren Baghdasaryan <surenb@google.com> > > Cc: Matthew Bobrowski <repnop@google.com> > > Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com> > > Cc: David Hildenbrand <david@redhat.com> > > Cc: Jan Kara <jack@suse.cz> > > Cc: Minchan Kim <minchan@kernel.org> > > Reviewed-by: Matthew Bobrowski <repnop@google.com> > > Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> > > --- > > /* v2 */ > > unchanged > > Acked-by: David Hildenbrand <david@redhat.com> Thanks! Christian
diff --git a/mm/madvise.c b/mm/madvise.c index 0734db8d53a7..8c927202bbe6 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1235,7 +1235,6 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, struct iovec iovstack[UIO_FASTIOV], iovec; struct iovec *iov = iovstack; struct iov_iter iter; - struct pid *pid; struct task_struct *task; struct mm_struct *mm; size_t total_len; @@ -1250,18 +1249,12 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, if (ret < 0) goto out; - pid = pidfd_get_pid(pidfd, &f_flags); - if (IS_ERR(pid)) { - ret = PTR_ERR(pid); + task = pidfd_get_task(pidfd, &f_flags); + if (IS_ERR(task)) { + ret = PTR_ERR(task); goto free_iov; } - task = get_pid_task(pid, PIDTYPE_PID); - if (!task) { - ret = -ESRCH; - goto put_pid; - } - if (!process_madvise_behavior_valid(behavior)) { ret = -EINVAL; goto release_task; @@ -1301,8 +1294,6 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, mmput(mm); release_task: put_task_struct(task); -put_pid: - put_pid(pid); free_iov: kfree(iov); out: diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 831340e7ad8b..70d399d5817e 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -1151,21 +1151,14 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) struct task_struct *p; unsigned int f_flags; bool reap = true; - struct pid *pid; long ret = 0; if (flags) return -EINVAL; - pid = pidfd_get_pid(pidfd, &f_flags); - if (IS_ERR(pid)) - return PTR_ERR(pid); - - task = get_pid_task(pid, PIDTYPE_TGID); - if (!task) { - ret = -ESRCH; - goto put_pid; - } + task = pidfd_get_task(pidfd, &f_flags); + if (IS_ERR(task)) + return PTR_ERR(task); /* * Make sure to choose a thread which still has a reference to mm @@ -1204,8 +1197,6 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) mmdrop(mm); put_task: put_task_struct(task); -put_pid: - put_pid(pid); return ret; #else return -ENOSYS;