signalfd: fill in ssi_int for posix timers and message queues
in [Kernel]
|
Prev: arch/tile: updates to hardwall code from community feedback.
Next: [PATCH v2] msm: gpio: Add set_wake support to msm7200a-gpio's irq_chip.
From: Davide Libenzi on 3 Jul 2010 15:20 On Fri, 2 Jul 2010, Nathan Lynch wrote: > If signalfd is used to consume a signal generated by a POSIX interval > timer or POSIX message queue, the ssi_int field does not reflect the > data (sigevent->sigev_value) supplied to timer_create(2) or > mq_notify(3). (The ssi_ptr field, however, is filled in.) > > This behavior differs from signalfd's treatment of sigqueue-generated > signals -- see the default case in signalfd_copyinfo. It also gives > results that differ from the case when a signal is handled > conventionally via a sigaction-registered handler. > > So, set signalfd_siginfo->ssi_int in the remaining cases (__SI_TIMER, > __SI_MESGQ) where ssi_ptr is set. > > Signed-off-by: Nathan Lynch <ntl(a)pobox.com> > --- > fs/signalfd.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/fs/signalfd.c b/fs/signalfd.c > index f329849..1c5a6ad 100644 > --- a/fs/signalfd.c > +++ b/fs/signalfd.c > @@ -88,6 +88,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, > err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid); > err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun); > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr); > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int); > break; > case __SI_POLL: > err |= __put_user(kinfo->si_band, &uinfo->ssi_band); > @@ -111,6 +112,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, > err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid); > err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid); > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr); > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int); > break; > default: I am fine with it, but I now noticed that signalfd_copyinfo() got out of sync from copy_siginfo_to_user(), which should match. Do you mind aligning that too, as part of your patch? An adding a comment on the lines of the one in copy_siginfo_to_user() to signalfd_copyinfo() too? If you do not want to, let me know and I'll do it. - Davide -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Nathan Lynch on 5 Jul 2010 08:30 Hello Davide, On Sat, 2010-07-03 at 12:09 -0700, Davide Libenzi wrote: > On Fri, 2 Jul 2010, Nathan Lynch wrote: > > > If signalfd is used to consume a signal generated by a POSIX interval > > timer or POSIX message queue, the ssi_int field does not reflect the > > data (sigevent->sigev_value) supplied to timer_create(2) or > > mq_notify(3). (The ssi_ptr field, however, is filled in.) > > > > This behavior differs from signalfd's treatment of sigqueue-generated > > signals -- see the default case in signalfd_copyinfo. It also gives > > results that differ from the case when a signal is handled > > conventionally via a sigaction-registered handler. > > > > So, set signalfd_siginfo->ssi_int in the remaining cases (__SI_TIMER, > > __SI_MESGQ) where ssi_ptr is set. > > > > Signed-off-by: Nathan Lynch <ntl(a)pobox.com> > > --- > > fs/signalfd.c | 2 ++ > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > diff --git a/fs/signalfd.c b/fs/signalfd.c > > index f329849..1c5a6ad 100644 > > --- a/fs/signalfd.c > > +++ b/fs/signalfd.c > > @@ -88,6 +88,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, > > err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid); > > err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun); > > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr); > > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int); > > break; > > case __SI_POLL: > > err |= __put_user(kinfo->si_band, &uinfo->ssi_band); > > @@ -111,6 +112,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, > > err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid); > > err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid); > > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr); > > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int); > > break; > > default: > > I am fine with it, but I now noticed that signalfd_copyinfo() got out of > sync from copy_siginfo_to_user(), which should match. > Do you mind aligning that too, as part of your patch? > An adding a comment on the lines of the one in copy_siginfo_to_user() to > signalfd_copyinfo() too? Sorry, I'm not sure I understand. Are you saying that copy_siginfo_to_user should have analogous lines added to assign to si_int? That's actually not necessary if I read the code correctly: in struct siginfo, si_ptr and si_int are members of a sigval union, so assigning to the former covers the latter. signalfd must assign both ssi_ptr and ssi_int since they occupy different locations in signalfd_siginfo. Perhaps the attached testcases make the problem (as I see it) more clear? The final assertion fails without this patch.
From: Davide Libenzi on 5 Jul 2010 14:30 On Mon, 5 Jul 2010, Nathan Lynch wrote: > Hello Davide, > > On Sat, 2010-07-03 at 12:09 -0700, Davide Libenzi wrote: > > On Fri, 2 Jul 2010, Nathan Lynch wrote: > > > > > If signalfd is used to consume a signal generated by a POSIX interval > > > timer or POSIX message queue, the ssi_int field does not reflect the > > > data (sigevent->sigev_value) supplied to timer_create(2) or > > > mq_notify(3). (The ssi_ptr field, however, is filled in.) > > > > > > This behavior differs from signalfd's treatment of sigqueue-generated > > > signals -- see the default case in signalfd_copyinfo. It also gives > > > results that differ from the case when a signal is handled > > > conventionally via a sigaction-registered handler. > > > > > > So, set signalfd_siginfo->ssi_int in the remaining cases (__SI_TIMER, > > > __SI_MESGQ) where ssi_ptr is set. > > > > > > Signed-off-by: Nathan Lynch <ntl(a)pobox.com> > > > --- > > > fs/signalfd.c | 2 ++ > > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > > > diff --git a/fs/signalfd.c b/fs/signalfd.c > > > index f329849..1c5a6ad 100644 > > > --- a/fs/signalfd.c > > > +++ b/fs/signalfd.c > > > @@ -88,6 +88,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, > > > err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid); > > > err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun); > > > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr); > > > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int); > > > break; > > > case __SI_POLL: > > > err |= __put_user(kinfo->si_band, &uinfo->ssi_band); > > > @@ -111,6 +112,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, > > > err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid); > > > err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid); > > > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr); > > > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int); > > > break; > > > default: > > > > I am fine with it, but I now noticed that signalfd_copyinfo() got out of > > sync from copy_siginfo_to_user(), which should match. > > Do you mind aligning that too, as part of your patch? > > An adding a comment on the lines of the one in copy_siginfo_to_user() to > > signalfd_copyinfo() too? > > Sorry, I'm not sure I understand. Are you saying that > copy_siginfo_to_user should have analogous lines added to assign to > si_int? That's actually not necessary if I read the code correctly: in > struct siginfo, si_ptr and si_int are members of a sigval union, so > assigning to the former covers the latter. signalfd must assign both > ssi_ptr and ssi_int since they occupy different locations in > signalfd_siginfo. > > Perhaps the attached testcases make the problem (as I see it) more > clear? The final assertion fails without this patch. Sorry, my bad. I had forgotten that siginfo had them in a union, so the different code in signalfd_copyinfo() is needed. Patch looks fine to me as is. - Davide -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Andrew Morton on 20 Jul 2010 18:50 On Fri, 02 Jul 2010 19:38:48 -0500 Nathan Lynch <ntl(a)pobox.com> wrote: > If signalfd is used to consume a signal generated by a POSIX interval > timer or POSIX message queue, the ssi_int field does not reflect the > data (sigevent->sigev_value) supplied to timer_create(2) or > mq_notify(3). (The ssi_ptr field, however, is filled in.) > > This behavior differs from signalfd's treatment of sigqueue-generated > signals -- see the default case in signalfd_copyinfo. It also gives > results that differ from the case when a signal is handled > conventionally via a sigaction-registered handler. > > So, set signalfd_siginfo->ssi_int in the remaining cases (__SI_TIMER, > __SI_MESGQ) where ssi_ptr is set. > This introduces an incompatibility between kernel versions. Someone develops and tests an application on 2.6.36 or later then ships it and lo, it malfunctions on 2.6.35 and earlier. Is there a way to avoid that? Don't think so. How should the more-awake-than-average application developer prevent this problem? Should he probe the syscall at runtime to determine its behaviour? He can't use the kernel version number because the kernel provider might have backported this patch into an earlier kernel. We can minimise the problem by backporting into -stable, and hoping that awake kernel packagers understand the issue, and backport the change as far as they can. So it's not 100% obvious that this change is desirable. Does the functionality which this patch adds justify the introduction of these problems? > --- > fs/signalfd.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/fs/signalfd.c b/fs/signalfd.c > index f329849..1c5a6ad 100644 > --- a/fs/signalfd.c > +++ b/fs/signalfd.c > @@ -88,6 +88,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, > err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid); > err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun); > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr); > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int); > break; hm, someone bollixed the __SI_TIMER indenting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Nathan Lynch on 20 Jul 2010 23:50
On Tue, 2010-07-20 at 15:42 -0700, Andrew Morton wrote: > On Fri, 02 Jul 2010 19:38:48 -0500 > Nathan Lynch <ntl(a)pobox.com> wrote: > > > If signalfd is used to consume a signal generated by a POSIX interval > > timer or POSIX message queue, the ssi_int field does not reflect the > > data (sigevent->sigev_value) supplied to timer_create(2) or > > mq_notify(3). (The ssi_ptr field, however, is filled in.) > > > > This behavior differs from signalfd's treatment of sigqueue-generated > > signals -- see the default case in signalfd_copyinfo. It also gives > > results that differ from the case when a signal is handled > > conventionally via a sigaction-registered handler. > > > > So, set signalfd_siginfo->ssi_int in the remaining cases (__SI_TIMER, > > __SI_MESGQ) where ssi_ptr is set. > > > > This introduces an incompatibility between kernel versions. Someone > develops and tests an application on 2.6.36 or later then ships it and > lo, it malfunctions on 2.6.35 and earlier. > > Is there a way to avoid that? Don't think so. > > How should the more-awake-than-average application developer prevent > this problem? Should he probe the syscall at runtime to determine its > behaviour? He can't use the kernel version number because the kernel > provider might have backported this patch into an earlier kernel. > > We can minimise the problem by backporting into -stable, and hoping > that awake kernel packagers understand the issue, and backport the > change as far as they can. And perhaps document it in the signalfd man page. This was done for commit 0859ab5 "signalfd: fix for incorrect SI_QUEUE user data reporting", which seems to a be a similar case. > So it's not 100% obvious that this change is desirable. Does the > functionality which this patch adds justify the introduction of these > problems? I think the change is desirable in that no user of the interface could reasonably expect the current behavior with respect to the ssi_int field, and that it reconciles signalfd's behavior with its design intentions. On the other hand, I noticed this discrepancy only because I was cribbing signalfd's data structures for checkpoint/restart, not because I am aware of any application that is affected, nor was I able to find one using Google's code search. It would be highly speculative of me to say that no application depends on the current behavior, but it is difficult to imagine a correctly functioning application that depends on it. Davide, any opinion here? > > fs/signalfd.c | 2 ++ > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > diff --git a/fs/signalfd.c b/fs/signalfd.c > > index f329849..1c5a6ad 100644 > > --- a/fs/signalfd.c > > +++ b/fs/signalfd.c > > @@ -88,6 +88,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, > > err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid); > > err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun); > > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr); > > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int); > > break; > > hm, someone bollixed the __SI_TIMER indenting. In kernel/signal.c::copy_siginfo_to_user() too :) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |