| Message ID | 20240701223935.3783951-2-andrii@kernel.org (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | uprobes: add batched register/unregister APIs and per-CPU RW semaphore | expand |
Sorry for the late reply. I'll try to read this version/discussion when I have time... yes, I have already promised this before, sorry :/ On 07/01, Andrii Nakryiko wrote: > > There is no task_struct passed into get_user_pages_remote() anymore, > drop the parts of comment mentioning NULL tsk, it's just confusing at > this point. Agreed. > @@ -2030,10 +2030,8 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) > goto out; > > /* > - * The NULL 'tsk' here ensures that any faults that occur here > - * will not be accounted to the task. 'mm' *is* current->mm, > - * but we treat this as a 'remote' access since it is > - * essentially a kernel access to the memory. > + * 'mm' *is* current->mm, but we treat this as a 'remote' access since > + * it is essentially a kernel access to the memory. > */ > result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page, NULL); OK, this makes it less confusing, so Acked-by: Oleg Nesterov <oleg@redhat.com> --------------------------------------------------------------------- but it still looks confusing to me. This code used to pass tsk = NULL only to avoid tsk->maj/min_flt++ in faultin_page(). But today mm_account_fault() increments these counters without checking FAULT_FLAG_REMOTE, mm == current->mm, so it seems it would be better to just use get_user_pages() and remove this comment? Oleg.
On Wed, Jul 3, 2024 at 4:40 AM Oleg Nesterov <oleg@redhat.com> wrote: > > Sorry for the late reply. I'll try to read this version/discussion > when I have time... yes, I have already promised this before, sorry :/ > > On 07/01, Andrii Nakryiko wrote: > > > > There is no task_struct passed into get_user_pages_remote() anymore, > > drop the parts of comment mentioning NULL tsk, it's just confusing at > > this point. > > Agreed. > > > @@ -2030,10 +2030,8 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) > > goto out; > > > > /* > > - * The NULL 'tsk' here ensures that any faults that occur here > > - * will not be accounted to the task. 'mm' *is* current->mm, > > - * but we treat this as a 'remote' access since it is > > - * essentially a kernel access to the memory. > > + * 'mm' *is* current->mm, but we treat this as a 'remote' access since > > + * it is essentially a kernel access to the memory. > > */ > > result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page, NULL); > > OK, this makes it less confusing, so > > Acked-by: Oleg Nesterov <oleg@redhat.com> > > > --------------------------------------------------------------------- > but it still looks confusing to me. This code used to pass tsk = NULL > only to avoid tsk->maj/min_flt++ in faultin_page(). > > But today mm_account_fault() increments these counters without checking > FAULT_FLAG_REMOTE, mm == current->mm, so it seems it would be better to > just use get_user_pages() and remove this comment? I don't know, it was a drive-by cleanup which I'm starting to regret already :) > > Oleg. >
On Wed, Jul 3, 2024 at 4:40 AM Oleg Nesterov <oleg@redhat.com> wrote: > > Sorry for the late reply. I'll try to read this version/discussion > when I have time... yes, I have already promised this before, sorry :/ > No worries, there will be v3 next week (I'm going on short PTO starting tomorrow). So you still have time. I appreciate you looking at it, though! > On 07/01, Andrii Nakryiko wrote: > > > > There is no task_struct passed into get_user_pages_remote() anymore, > > drop the parts of comment mentioning NULL tsk, it's just confusing at > > this point. > > Agreed. > > > @@ -2030,10 +2030,8 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) > > goto out; > > > > /* > > - * The NULL 'tsk' here ensures that any faults that occur here > > - * will not be accounted to the task. 'mm' *is* current->mm, > > - * but we treat this as a 'remote' access since it is > > - * essentially a kernel access to the memory. > > + * 'mm' *is* current->mm, but we treat this as a 'remote' access since > > + * it is essentially a kernel access to the memory. > > */ > > result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page, NULL); > > OK, this makes it less confusing, so > > Acked-by: Oleg Nesterov <oleg@redhat.com> > > > --------------------------------------------------------------------- > but it still looks confusing to me. This code used to pass tsk = NULL > only to avoid tsk->maj/min_flt++ in faultin_page(). > > But today mm_account_fault() increments these counters without checking > FAULT_FLAG_REMOTE, mm == current->mm, so it seems it would be better to > just use get_user_pages() and remove this comment? > > Oleg. >
On 07/03, Oleg Nesterov wrote: > > > /* > > - * The NULL 'tsk' here ensures that any faults that occur here > > - * will not be accounted to the task. 'mm' *is* current->mm, > > - * but we treat this as a 'remote' access since it is > > - * essentially a kernel access to the memory. > > + * 'mm' *is* current->mm, but we treat this as a 'remote' access since > > + * it is essentially a kernel access to the memory. > > */ > > result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page, NULL); > > OK, this makes it less confusing, so > > Acked-by: Oleg Nesterov <oleg@redhat.com> > > --------------------------------------------------------------------- > but it still looks confusing to me. This code used to pass tsk = NULL > only to avoid tsk->maj/min_flt++ in faultin_page(). > > But today mm_account_fault() increments these counters without checking > FAULT_FLAG_REMOTE, mm == current->mm, so it seems it would be better to > just use get_user_pages() and remove this comment? Well, yes, it still looks confusing, imo. Andrii, I hope you won't mind if I redo/resend this and the next cleanup? The next one only updates the comment above uprobe_write_opcode(), but it would be nice to explain mmap_write_lock() in register_for_each_vma(). Oleg.
On Wed, Jul 10, 2024 at 6:33 AM Oleg Nesterov <oleg@redhat.com> wrote: > > On 07/03, Oleg Nesterov wrote: > > > > > /* > > > - * The NULL 'tsk' here ensures that any faults that occur here > > > - * will not be accounted to the task. 'mm' *is* current->mm, > > > - * but we treat this as a 'remote' access since it is > > > - * essentially a kernel access to the memory. > > > + * 'mm' *is* current->mm, but we treat this as a 'remote' access since > > > + * it is essentially a kernel access to the memory. > > > */ > > > result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page, NULL); > > > > OK, this makes it less confusing, so > > > > Acked-by: Oleg Nesterov <oleg@redhat.com> > > > > --------------------------------------------------------------------- > > but it still looks confusing to me. This code used to pass tsk = NULL > > only to avoid tsk->maj/min_flt++ in faultin_page(). > > > > But today mm_account_fault() increments these counters without checking > > FAULT_FLAG_REMOTE, mm == current->mm, so it seems it would be better to > > just use get_user_pages() and remove this comment? > > Well, yes, it still looks confusing, imo. > > Andrii, I hope you won't mind if I redo/resend this and the next cleanup? > > The next one only updates the comment above uprobe_write_opcode(), but > it would be nice to explain mmap_write_lock() in register_for_each_vma(). > I don't mind a bit, thanks for sending the patches! > Oleg. > >
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 99be2adedbc0..081821fd529a 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -2030,10 +2030,8 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) goto out; /* - * The NULL 'tsk' here ensures that any faults that occur here - * will not be accounted to the task. 'mm' *is* current->mm, - * but we treat this as a 'remote' access since it is - * essentially a kernel access to the memory. + * 'mm' *is* current->mm, but we treat this as a 'remote' access since + * it is essentially a kernel access to the memory. */ result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page, NULL); if (result < 0)
There is no task_struct passed into get_user_pages_remote() anymore, drop the parts of comment mentioning NULL tsk, it's just confusing at this point. Signed-off-by: Andrii Nakryiko <andrii@kernel.org> --- kernel/events/uprobes.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)