Currently timer_free() is a simple wrapper for g_free().  This means
that the timer being freed must not be currently active, as otherwise
QEMU might crash later when the active list is processed and still
has a pointer to freed memory on it.  As a result almost all calls to
timer_free() are preceded by a timer_del() call, as can be seen in
the output of
  git grep -B1 '\<timer_free\>'

This is unfortunate API design as it makes it easy to accidentally
misuse (by forgetting the timer_del()), and the correct use is
annoyingly verbose.

Patch 1 makes timer_free() call timer_del() if the timer is active.
Patch 2 is a Coccinelle script to remove any timer_del() calls
that are immediately before the timer_free().
Patch 3 is the result of running the Coccinelle script on the
whole tree.
Patch 4 makes a by-hand cleanup of a bit of the Arm CPU code
not caught by Coccinelle because it included a pointless
timer_deinit() between timer_del() and timer_free().

I could split up patch 3, but for 58 deleted lines over 42 files
created entirely automatedly, it seemed to me to be simpler as one
patch.

Changes v1->v2:
 * patch 1: unconditionally call timer_del() rather than trying
   to be clever
 * patch 4: new patch

thanks
-- PMM

Peter Maydell (4):
  util/qemu-timer: Make timer_free() imply timer_del()
  scripts/coccinelle: New script to remove unnecessary timer_del() calls
  Remove superfluous timer_del() calls
  target/arm: Remove timer_del()/timer_deinit() before timer_free()

 scripts/coccinelle/timer-del-timer-free.cocci | 18 +++++++++++++
 include/qemu/timer.h                          | 25 +++++++++++--------
 block/iscsi.c                                 |  2 --
 block/nbd.c                                   |  1 -
 block/qcow2.c                                 |  1 -
 hw/block/nvme.c                               |  2 --
 hw/char/serial.c                              |  2 --
 hw/char/virtio-serial-bus.c                   |  2 --
 hw/ide/core.c                                 |  1 -
 hw/input/hid.c                                |  1 -
 hw/intc/apic.c                                |  1 -
 hw/intc/ioapic.c                              |  1 -
 hw/ipmi/ipmi_bmc_extern.c                     |  1 -
 hw/net/e1000.c                                |  3 ---
 hw/net/e1000e_core.c                          |  8 ------
 hw/net/pcnet-pci.c                            |  1 -
 hw/net/rtl8139.c                              |  1 -
 hw/net/spapr_llan.c                           |  1 -
 hw/net/virtio-net.c                           |  2 --
 hw/s390x/s390-pci-inst.c                      |  1 -
 hw/sd/sd.c                                    |  1 -
 hw/sd/sdhci.c                                 |  2 --
 hw/usb/dev-hub.c                              |  1 -
 hw/usb/hcd-ehci.c                             |  1 -
 hw/usb/hcd-ohci-pci.c                         |  1 -
 hw/usb/hcd-uhci.c                             |  1 -
 hw/usb/hcd-xhci.c                             |  1 -
 hw/usb/redirect.c                             |  1 -
 hw/vfio/display.c                             |  1 -
 hw/virtio/vhost-vsock-common.c                |  1 -
 hw/virtio/virtio-balloon.c                    |  1 -
 hw/virtio/virtio-rng.c                        |  1 -
 hw/watchdog/wdt_diag288.c                     |  1 -
 hw/watchdog/wdt_i6300esb.c                    |  1 -
 migration/colo.c                              |  1 -
 monitor/hmp-cmds.c                            |  1 -
 net/announce.c                                |  1 -
 net/colo-compare.c                            |  1 -
 net/slirp.c                                   |  1 -
 replay/replay-debugging.c                     |  1 -
 target/arm/cpu.c                              |  2 --
 target/s390x/cpu.c                            |  2 --
 ui/console.c                                  |  1 -
 ui/spice-core.c                               |  1 -
 util/throttle.c                               |  1 -
 45 files changed, 32 insertions(+), 71 deletions(-)
 create mode 100644 scripts/coccinelle/timer-del-timer-free.cocci

-- 
2.20.1

On 12/15/20 4:41 PM, Peter Maydell wrote:
> Currently timer_free() is a simple wrapper for g_free().  This means
> that the timer being freed must not be currently active, as otherwise
> QEMU might crash later when the active list is processed and still
> has a pointer to freed memory on it.  As a result almost all calls to
> timer_free() are preceded by a timer_del() call, as can be seen in
> the output of
>   git grep -B1 '\<timer_free\>'
> 
> This is unfortunate API design as it makes it easy to accidentally
> misuse (by forgetting the timer_del()), and the correct use is
> annoyingly verbose.
> 
> Patch 1 makes timer_free() call timer_del() if the timer is active.
> Patch 2 is a Coccinelle script to remove any timer_del() calls
> that are immediately before the timer_free().
> Patch 3 is the result of running the Coccinelle script on the
> whole tree.
> Patch 4 makes a by-hand cleanup of a bit of the Arm CPU code
> not caught by Coccinelle because it included a pointless
> timer_deinit() between timer_del() and timer_free().
> 
> I could split up patch 3, but for 58 deleted lines over 42 files
> created entirely automatedly, it seemed to me to be simpler as one
> patch.
> 
> Changes v1->v2:
>  * patch 1: unconditionally call timer_del() rather than trying
>    to be clever
>  * patch 4: new patch
> 
> thanks
> -- PMM
> 
> Peter Maydell (4):
>   util/qemu-timer: Make timer_free() imply timer_del()
>   scripts/coccinelle: New script to remove unnecessary timer_del() calls
>   Remove superfluous timer_del() calls
>   target/arm: Remove timer_del()/timer_deinit() before timer_free()
> 
>  scripts/coccinelle/timer-del-timer-free.cocci | 18 +++++++++++++
>  include/qemu/timer.h                          | 25 +++++++++++--------
>  block/iscsi.c                                 |  2 --
>  block/nbd.c                                   |  1 -
>  block/qcow2.c                                 |  1 -
>  hw/block/nvme.c                               |  2 --
>  hw/char/serial.c                              |  2 --
>  hw/char/virtio-serial-bus.c                   |  2 --
>  hw/ide/core.c                                 |  1 -
>  hw/input/hid.c                                |  1 -
>  hw/intc/apic.c                                |  1 -
>  hw/intc/ioapic.c                              |  1 -
>  hw/ipmi/ipmi_bmc_extern.c                     |  1 -
>  hw/net/e1000.c                                |  3 ---
>  hw/net/e1000e_core.c                          |  8 ------
>  hw/net/pcnet-pci.c                            |  1 -
>  hw/net/rtl8139.c                              |  1 -
>  hw/net/spapr_llan.c                           |  1 -
>  hw/net/virtio-net.c                           |  2 --
>  hw/s390x/s390-pci-inst.c                      |  1 -
>  hw/sd/sd.c                                    |  1 -
>  hw/sd/sdhci.c                                 |  2 --
>  hw/usb/dev-hub.c                              |  1 -
>  hw/usb/hcd-ehci.c                             |  1 -
>  hw/usb/hcd-ohci-pci.c                         |  1 -
>  hw/usb/hcd-uhci.c                             |  1 -
>  hw/usb/hcd-xhci.c                             |  1 -
>  hw/usb/redirect.c                             |  1 -
>  hw/vfio/display.c                             |  1 -
>  hw/virtio/vhost-vsock-common.c                |  1 -
>  hw/virtio/virtio-balloon.c                    |  1 -
>  hw/virtio/virtio-rng.c                        |  1 -
>  hw/watchdog/wdt_diag288.c                     |  1 -
>  hw/watchdog/wdt_i6300esb.c                    |  1 -
>  migration/colo.c                              |  1 -
>  monitor/hmp-cmds.c                            |  1 -
>  net/announce.c                                |  1 -
>  net/colo-compare.c                            |  1 -
>  net/slirp.c                                   |  1 -
>  replay/replay-debugging.c                     |  1 -
>  target/arm/cpu.c                              |  2 --
>  target/s390x/cpu.c                            |  2 --
>  ui/console.c                                  |  1 -
>  ui/spice-core.c                               |  1 -
>  util/throttle.c                               |  1 -
>  45 files changed, 32 insertions(+), 71 deletions(-)
>  create mode 100644 scripts/coccinelle/timer-del-timer-free.cocci
> 

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

On Tue, 15 Dec 2020 at 15:41, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> Currently timer_free() is a simple wrapper for g_free().  This means
> that the timer being freed must not be currently active, as otherwise
> QEMU might crash later when the active list is processed and still
> has a pointer to freed memory on it.  As a result almost all calls to
> timer_free() are preceded by a timer_del() call, as can be seen in
> the output of
>   git grep -B1 '\<timer_free\>'
>
> This is unfortunate API design as it makes it easy to accidentally
> misuse (by forgetting the timer_del()), and the correct use is
> annoyingly verbose.

I'll take this via the target-arm queue. Thanks to all for the review.

-- PMM