kernel/linux.git/drivers/s390/cio/css.c, branch linux-4.4.y

s390/cio: add cond_resched() in the slow_eval_known_fn() loop

2020-09-03T09:19:25+00:00

[ Upstream commit 0b8eb2ee9da1e8c9b8082f404f3948aa82a057b2 ] The scanning through subchannels during the time of an event could take significant amount of time in case of platforms with lots of known subchannels. This might result in higher scheduling latencies for other tasks especially on systems with a single CPU. Add cond_resched() call, as the loop in slow_eval_known_fn() can be executed for a longer duration. Reviewed-by: Peter Oberparleiter Signed-off-by: Vineeth Vijayan Signed-off-by: Heiko Carstens Signed-off-by: Sasha Levin

s390/cio: exclude subchannels with no parent from pseudo check

2019-10-17T20:40:53+00:00

commit ab5758848039de9a4b249d46e4ab591197eebaf2 upstream. ccw console is created early in start_kernel and used before css is initialized or ccw console subchannel is registered. Until then console subchannel does not have a parent. For that reason assume subchannels with no parent are not pseudo subchannels. This fixes the following kasan finding: BUG: KASAN: global-out-of-bounds in sch_is_pseudo_sch+0x8e/0x98 Read of size 8 at addr 00000000000005e8 by task swapper/0/0 CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.3.0-rc8-07370-g6ac43dd12538 #2 Hardware name: IBM 2964 NC9 702 (z/VM 6.4.0) Call Trace: ([<000000000012cd76>] show_stack+0x14e/0x1e0) [<0000000001f7fb44>] dump_stack+0x1a4/0x1f8 [<00000000007d7afc>] print_address_description+0x64/0x3c8 [<00000000007d75f6>] __kasan_report+0x14e/0x180 [<00000000018a2986>] sch_is_pseudo_sch+0x8e/0x98 [<000000000189b950>] cio_enable_subchannel+0x1d0/0x510 [<00000000018cac7c>] ccw_device_recognition+0x12c/0x188 [<0000000002ceb1a8>] ccw_device_enable_console+0x138/0x340 [<0000000002cf1cbe>] con3215_init+0x25e/0x300 [<0000000002c8770a>] console_init+0x68a/0x9b8 [<0000000002c6a3d6>] start_kernel+0x4fe/0x728 [<0000000000100070>] startup_continue+0x70/0xd0 Cc: stable@vger.kernel.org Reviewed-by: Sebastian Ott Signed-off-by: Vasily Gorbik Signed-off-by: Greg Kroah-Hartman

s390/cio: simplify css_generate_pgid

2015-11-09T08:10:48+00:00

Simplify the css_generate_pgid code by using stap() independent of CONFIG_SMP. For !CONFIG_SMP builds stap() will deliver the address of the cpu we IPL'ed from (which can be != 0). Note: the ifdef was likely added to be compatible with _very_ old machines which we don't support anyway. Reviewed-by: Peter Oberparleiter Signed-off-by: Sebastian Ott Signed-off-by: Martin Schwidefsky

s390/css: unneeded initialization in for_each_subchannel

2015-11-03T13:40:49+00:00

The ret variable is always set by the fn function. There is no need to initialize it. Signed-off-by: Pierre Morel Reviewed-By: Sascha Silbe Acked-by: Cornelia Huck Signed-off-by: Martin Schwidefsky

s390/cio: reactivate cmf after hibernate

2015-10-14T12:32:04+00:00

During resume from hibernate we already reenable measurement block updates on a per device basis. In addition to that we also need to activate channel measurement globally using the set channel monitor instruction. Signed-off-by: Sebastian Ott Reviewed-by: Martin Schwidefsky Reviewed-by: Cornelia Huck Signed-off-by: Martin Schwidefsky

s390/css: Prevent unnecessary allocation in subchannel loop

2013-12-16T13:37:42+00:00

Subchannel looping function for_each_subchannel_staged() allocates a subchannel-ID-bitmap to efficiently iterate over the list of known and unknown subchannels. Since this function is also used to iterate over known-subchannels only, optimize that case by not requiring the ID-bitmap allocation and falling back to simple bus_for_each_dev() looping. Signed-off-by: Peter Oberparleiter Reviewed-by: Sebastian Ott Signed-off-by: Martin Schwidefsky

s390/cio: Delay scan for newly available I/O devices

2013-12-16T13:37:41+00:00

The CIO layer scans for newly available I/O devices by performing a scan of available subchannels using the Store Subchannel (STSCH) instruction. Performing too many STSCH instructions in a tight loop can cause high Hypervisor overhead which can negatively impact the performance of the virtual machine as a whole. A subchannel scan is triggered for example during a hardware event that indicates that a channel path has become available. It is also triggered by the DASD device driver for each device that is set online. This patch reduces the number of STSCH instructions being performed by delaying the start of the actual subchannel scan by 1 second. Multiple scan requests that are scheduled during this time will be merged into a single scan loop. The trade-off consists of a short delay that is introduced between the time that the event is processed and a newly available device becoming usable. This delay should be acceptable since it only affects devices that have not been in use before. Signed-off-by: Peter Oberparleiter Reviewed-by: Sebastian Ott Signed-off-by: Martin Schwidefsky

s390/cio: Relax subchannel scan loop

2013-12-16T13:37:40+00:00

The CIO layer scans for newly available I/O devices by performing a scan of available subchannels using the Store Subchannel (STSCH) instruction. This processing can take a significant amount of time during which no other task can run on the same CPU (unless CONFIG_PREEMPT has been enabled). As a result, scheduling latencies for other tasks are increased noticeably, especially on a single-CPU system. Fix this problem by explicitly allowing other tasks to be scheduled each time a subchannel has been processed. Signed-off-by: Peter Oberparleiter Reviewed-by: Sebastian Ott Signed-off-by: Martin Schwidefsky

s390/cio: fix unlocked access of global bitmap

2013-08-30T06:57:22+00:00

Access to the slow_subchannel_set has to be secured via the slow_subchannel_lock. Signed-off-by: Sebastian Ott Signed-off-by: Martin Schwidefsky

s390: replace strict_strtoul() with kstrtoul()

2013-08-22T10:20:00+00:00

The usage of strict_strtoul() is not preferred, because strict_strtoul() is obsolete. Thus, kstrtoul() should be used. Signed-off-by: Jingoo Han Signed-off-by: Heiko Carstens Signed-off-by: Martin Schwidefsky