CVS commit: src/sys

["Ryota Ozaki" <ozaki-r%netbsd.org@localhost>]

Module Name:    src
Committed By:   ozaki-r
Date:           Wed Dec  6 09:03:13 UTC 2017

Modified Files:
        src/sys/dev/pci: if_wm.c
        src/sys/net: if.c if.h

Log Message:
Make if_timer MP-safe if IFEF_MPSAFE

if_timer, a counter used by if_watchdog (if_slowtimo), can be modified in
if_watchdog and if_start and/or interrupt handlers of some device drivers. All
such accesses were serialized by KERNEL_LOCK. If IFEF_MPSAFE is enabled,
KERNEL_LOCK of if_start (and perhaps interrupt handlers) is omitted and if_timer
becomes racy.

Fix the race condition by protecting if_timer by a spin mutex. if_watchdog_reset
and if_watchdog_stop are introduced to ensure to take the mutex on accessing
if_timer. Interface with IFEF_MPSAFE enabled must use the functions.

In addition, if_watchdog callout is now set CALLOUT_MPSAFE if IFEF_MPSAFE. It
means that if_watchdog implemented by a driver must be MP-safe if the driver is
set IFEF_MPSAFE.

Currenlty interfaces with IFEF_MPSAFE implementing if_watchdog and accessing
if_timer in if_start and interrupt handlers are only wm(4). wm is changed to
use the functions. (Its watchdog handler (wm_watchdog) is already MP-safe.

These contracts will be written somewhere in a further commit.

Note that the spin mutex is now ifp->if_snd.ifq_lock to avoid adding another
spin mutex to each interface. For now reusing it isn't problematic (see the
comment to know why) thought if that does matter in the future, feel free to
replace it with a new spin mutex. It's easy to do.


To generate a diff of this commit:
cvs rdiff -u -r1.546 -r1.547 src/sys/dev/pci/if_wm.c
cvs rdiff -u -r1.404 -r1.405 src/sys/net/if.c
cvs rdiff -u -r1.248 -r1.249 src/sys/net/if.h

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.