# 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 # 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 # Reported-and-tested-by: Josef Griebichler # Reported-by: Mauro Carvalho Chehab # Cc: Alan Stern # Cc: Greg Kroah-Hartman # Cc: Eric Dumazet # Cc: Ingo Molnar # Signed-off-by: Linus Torvalds # < /opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-gcc --version # < git log --format=%s --max-count=1 3c53776e29f81719efcf8f7a6e30cdf753bee94d # < make -s -j 10 ARCH=powerpc O=/kisskb/build/linus_mpc512x_defconfig_powerpc CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux- mpc512x_defconfig # make -s -j 10 ARCH=powerpc O=/kisskb/build/linus_mpc512x_defconfig_powerpc CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux- /kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl': /kisskb/src/kernel/printk/printk.c:183:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/base/regmap/regmap.c: In function 'regmap_raw_read': /kisskb/src/drivers/base/regmap/regmap.c:2497:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/base/regmap/regmap.c: In function '_regmap_raw_write': /kisskb/src/drivers/base/regmap/regmap.c:1819:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c: In function 'proc_reg_open': /kisskb/src/include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c:339:21: note: 'pdeo' was declared here INFO: Uncompressed kernel (size 0x5cd194) overlaps the address of the wrapper(0x400000) INFO: Fixing the link_address of wrapper to (0x600000) Image Name: Linux-4.18.0-rc5-g3c53776 Created: Wed Jul 18 11:14:46 2018 Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 2953763 Bytes = 2884.53 kB = 2.82 MB Load Address: 00000000 Entry Point: 00000000 Completed OK # rm -rf /kisskb/build/linus_mpc512x_defconfig_powerpc # Build took: 0:00:46.349384