Thomas Gleixner abd57a700e stop_machine: Mark per cpu stopper enabled early ... commit 14e568e78 (stop_machine: Use smpboot threads) introduced the following regression: Before this commit the stopper enabled bit was set in the online notifier. CPU0 CPU1 cpu_up cpu online hotplug_notifier(ONLINE) stopper(CPU1)->enabled = true; ... stop_machine() The conversion to smpboot threads moved the enablement to the wakeup path of the parked thread. The majority of users seem to have the following working order: CPU0 CPU1 cpu_up cpu online unpark_threads() wakeup(stopper[CPU1]) .... stopper thread runs stopper(CPU1)->enabled = true; stop_machine() But Konrad and Sander have observed: CPU0 CPU1 cpu_up cpu online unpark_threads() wakeup(stopper[CPU1]) .... stop_machine() stopper thread runs stopper(CPU1)->enabled = true; Now the stop machinery kicks CPU0 into the stop loop, where it gets stuck forever because the queue code saw stopper(CPU1)->enabled == false, so CPU0 waits for CPU1 to enter stomp_machine, but the CPU1 stopper work got discarded due to enabled == false. Add a pre_unpark function to the smpboot thread descriptor and call it before waking the thread. This fixes the problem at hand, but the stop_machine code should be more robust. The stopper->enabled flag smells fishy at best. Thanks to Konrad for going through a loop of debug patches and providing the information to decode this issue. Change-Id: I636875cf71ea5c5315eb0eb8599a8ebb9eadabf8 Reported-and-tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Reported-and-tested-by: Sander Eikelenboom <linux@eikelenboom.it> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1302261843240.22263@ionos Signed-off-by: Thomas Gleixner <tglx@linutronix.de>		2016-10-29 23:12:39 +08:00
..
acpi
asm-generic	crypto: create generic version of ablk_helper	2016-10-29 23:12:13 +08:00
crypto	crypto: sha512 - Expose generic sha512 routine to be callable from other modules	2016-10-29 23:12:14 +08:00
drm
keys	KEYS: Permit in-place link replacement in keyring list	2016-10-29 23:12:12 +08:00
linux	stop_machine: Mark per cpu stopper enabled early	2016-10-29 23:12:39 +08:00
math-emu
media	Fix header list when building with Android	2016-10-29 23:12:09 +08:00
misc
mtd
net	ipv6: clean up anycast when an interface is destroyed	2016-10-29 23:12:33 +08:00
pcmcia
rdma
rxrpc
scsi
sound
target
trace	f2fs: trace old block address for CoWed page	2016-10-29 23:12:32 +08:00
video
xen
Kbuild