# git rev-parse -q --verify 3c53776e29f81719efcf8f7a6e30cdf753bee94d^{commit}
3c53776e29f81719efcf8f7a6e30cdf753bee94d
already have revision, skipping fetch
# git checkout -q -f -B kisskb 3c53776e29f81719efcf8f7a6e30cdf753bee94d
# git clean -qxdf
# < git log -1
# commit 3c53776e29f81719efcf8f7a6e30cdf753bee94d
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Mon Jan 8 11:51:04 2018 -0800
# 
#     Mark HI and TASKLET softirq synchronous
#     
#     Way back in 4.9, we committed 4cd13c21b207 ("softirq: Let ksoftirqd do
#     its job"), and ever since we've had small nagging issues with it.  For
#     example, we've had:
#     
#       1ff688209e2e ("watchdog: core: make sure the watchdog_worker is not deferred")
#       8d5755b3f77b ("watchdog: softdog: fire watchdog even if softirqs do not get to run")
#       217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()")
#     
#     all of which worked around some of the effects of that commit.
#     
#     The DVB people have also complained that the commit causes excessive USB
#     URB latencies, which seems to be due to the USB code using tasklets to
#     schedule USB traffic.  This seems to be an issue mainly when already
#     living on the edge, but waiting for ksoftirqd to handle it really does
#     seem to cause excessive latencies.
#     
#     Now Hanna Hawa reports that this issue isn't just limited to USB URB and
#     DVB, but also causes timeout problems for the Marvell SoC team:
#     
#      "I'm facing kernel panic issue while running raid 5 on sata disks
#       connected to Macchiatobin (Marvell community board with Armada-8040
#       SoC with 4 ARMv8 cores of CA72) Raid 5 built with Marvell DMA engine
#       and async_tx mechanism (ASYNC_TX_DMA [=y]); the DMA driver (mv_xor_v2)
#       uses a tasklet to clean the done descriptors from the queue"
#     
#     The latency problem causes a panic:
#     
#       mv_xor_v2 f0400000.xor: dma_sync_wait: timeout!
#       Kernel panic - not syncing: async_tx_quiesce: DMA error waiting for transaction
#     
#     We've discussed simply just reverting the original commit entirely, and
#     also much more involved solutions (with per-softirq threads etc).  This
#     patch is intentionally stupid and fairly limited, because the issue
#     still remains, and the other solutions either got sidetracked or had
#     other issues.
#     
#     We should probably also consider the timer softirqs to be synchronous
#     and not be delayed to ksoftirqd (since they were the issue with the
#     earlier watchdog problems), but that should be done as a separate patch.
#     This does only the tasklet cases.
#     
#     Reported-and-tested-by: Hanna Hawa <hannah@marvell.com>
#     Reported-and-tested-by: Josef Griebichler <griebichler.josef@gmx.at>
#     Reported-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
#     Cc: Alan Stern <stern@rowland.harvard.edu>
#     Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
#     Cc: Eric Dumazet <edumazet@google.com>
#     Cc: Ingo Molnar <mingo@kernel.org>
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-gcc --version
# < git log --format=%s --max-count=1 3c53776e29f81719efcf8f7a6e30cdf753bee94d
# < make -s -j 48 ARCH=xtensa O=/kisskb/build/linus_xtensa-defconfig_xtensa CROSS_COMPILE=/opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-  defconfig
drivers/staging/mt7621-dts/Kconfig:4:warning: 'BUILTIN_DTB' has wrong type. 'select' only accept arguments of bool and tristate type
# make -s -j 48 ARCH=xtensa O=/kisskb/build/linus_xtensa-defconfig_xtensa CROSS_COMPILE=/opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-  
drivers/staging/mt7621-dts/Kconfig:4:warning: 'BUILTIN_DTB' has wrong type. 'select' only accept arguments of bool and tristate type
<stdin>:1332:2: warning: #warning syscall io_pgetevents not implemented [-Wcpp]
<stdin>:1335:2: warning: #warning syscall rseq not implemented [-Wcpp]
Completed OK
# rm -rf /kisskb/build/linus_xtensa-defconfig_xtensa
# Build took: 0:00:25.363576