Messages in this thread | | | Date | Tue, 28 Nov 2023 10:30:49 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH] kthread: kthread_should_stop() checks if we're a kthread |
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Adding Andrew into Cc. He usually takes changes in kernel/kthread.c.
On Mon 2023-11-20 17:15:03, Kent Overstreet wrote: > bcachefs has a fair amount of code that may or may not be running from a > kthread (it may instead be called by a userspace ioctl); having > kthread_should_stop() check if we're a kthread enables a fair bit of > cleanup and makes it safer to use. > > Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev> > --- > kernel/kthread.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/kthread.c b/kernel/kthread.c > index 1eea53050bab..fe6090ddf414 100644 > --- a/kernel/kthread.c > +++ b/kernel/kthread.c > @@ -155,7 +155,8 @@ void free_kthread_struct(struct task_struct *k) > */ > bool kthread_should_stop(void) > { > - return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags); > + return (current->flags & PF_KTHREAD) && > + test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags); > } > EXPORT_SYMBOL(kthread_should_stop);
I agree that it makes the API more safe because &to_kthread(current) is NULL when the process is not a kthread.
Well, I do not like the idea of quietly ignoring a misuse of the kthread_*() API. I would personally prefer to do:
// define this in include/linux/kthread.h static inline bool in_kthread(void) { return current->flags & PF_KTHREAD }
// add WARN() into kthread_should_stop() bool kthread_should_stop(void) { if (WARN_ON_ONCE(!in_kthread)) return false;
return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags); } EXPORT_SYMBOL(kthread_should_stop);
And use the following in bcachefs() code:
if (in_kthread() && kthread_should_stop()) goto exit;
Is see several advantages:
+ It will warn when the API is misused.
+ It will be more clear that the bcachefs code might be used in both kthread and userspace code.
+ in_kthread() might be used around other code which is needed only when the process is a kthread.
+ Similar check and WARN() might be used also in the other kthread() API.
Best Regards, Petr
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