From: Darren Hart <dvhltc@us.ibm.com>
To: linuxppc-dev@ozlabs.org
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
Gautham R Shenoy <ego@in.ibm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Will Schmidt <willschm@us.ibm.com>,
Paul Mackerras <paulus@samba.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH][RFC] preempt_count corruption across H_CEDE call with CONFIG_PREEMPT on pseries
Date: Thu, 22 Jul 2010 11:24:13 -0700 [thread overview]
Message-ID: <4C488CCD.60004@us.ibm.com> (raw)
While testing CPU offline/online, we hit various preempt_count related
bugs. Various hacks have been employed for several theoretical corner
cases. One situation however is perfectly repeatable on 2.6.33.6 with
CONFIG_PREEMPT=y.
BUG: scheduling while atomic: swapper/0/0x00000065
Modules linked in: autofs4 sunrpc ipv6 dm_mirror dm_region_hash dm_log
dm_mod ehea sg ext4 jbd2 mbcache sd_mod crc_t10dif ibmvscsic
scsi_transport_srp scsi_tgt [last unloaded: scsi_wait_scan]
Call Trace:
[c00000010e9e39f0] [c0000000000144d4] .show_stack+0x74/0x1c0 (unreliable)
[c00000010e9e3aa0] [c00000000007a680] .__schedule_bug+0xa0/0xb0
[c00000010e9e3b30] [c00000000056dea4] .schedule+0x7a4/0xd60
[c00000010e9e3cd0] [c000000000016be8] .cpu_idle+0x1f8/0x220
[c00000010e9e3d80] [c00000000057d858] .start_secondary+0x388/0x3c0
[c00000010e9e3e30] [c000000000008278] .start_secondary_resume+0x10/0x14
With some instrumentation we were able to determine that the
preempt_count() appears to change across the extended_cede_processor()
call. Specifically across the plpar_hcall_norets(H_CEDE) call. On
PREEMPT_RT we call this with preempt_count=1 and return with
preempt_count=0xffffffff. On mainline with CONFIG_PREEMPT=y, the value
is different (0x65) but is still incorrect.
Also of interest is that this path
cpu_idle()->cpu_die()->pseries_mach_cpu_die() to start_secondary()
enters with a preempt_count=1 if it wasn't corrupted across the hcall.
The early boot path from _start however appears to call
start_secondary() with a preempt_count of 0.
The following patch is most certainly not correct, but it does eliminate
the situation on mainline 100% of the time (there is still a 25%
reproduction rate on PREEMPT_RT). Can someone comment on:
1) How can the preempt_count() get mangled across the H_CEDE hcall?
2) Should we call preempt_enable() in cpu_idle() prior to cpu_die() ?
Hacked-up-by: Darren Hart <dvhltc@us.ibm.com>
Index: linux-2.6.33.6/arch/powerpc/platforms/pseries/hotplug-cpu.c
===================================================================
--- linux-2.6.33.6.orig/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ linux-2.6.33.6/arch/powerpc/platforms/pseries/hotplug-cpu.c
@@ -138,6 +138,7 @@ static void pseries_mach_cpu_die(void)
* Kernel stack will be reset and start_secondary()
* will be called to continue the online operation.
*/
+ preempt_count() = 0;
start_secondary_resume();
}
}
--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
next reply other threads:[~2010-07-22 18:24 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-22 18:24 Darren Hart [this message]
2010-07-22 18:36 ` [PATCH][RFC] preempt_count corruption across H_CEDE call with CONFIG_PREEMPT on pseries Darren Hart
2010-07-22 18:38 ` Thomas Gleixner
2010-08-10 22:36 ` Darren Hart
2010-07-22 22:25 ` Benjamin Herrenschmidt
2010-07-22 23:57 ` Darren Hart
2010-07-23 4:44 ` Darren Hart
2010-07-23 5:08 ` Vaidyanathan Srinivasan
2010-07-23 5:11 ` Benjamin Herrenschmidt
2010-07-23 7:07 ` Vaidyanathan Srinivasan
2010-08-05 4:45 ` Darren Hart
2010-08-05 11:06 ` Vaidyanathan Srinivasan
2010-08-05 12:26 ` Thomas Gleixner
2010-07-23 5:09 ` Benjamin Herrenschmidt
2010-08-06 2:19 ` Darren Hart
2010-08-06 5:09 ` Vaidyanathan Srinivasan
2010-08-06 7:13 ` Darren Hart
2010-07-23 14:39 ` Will Schmidt
2010-08-04 13:44 ` Darren Hart
2010-08-19 15:58 ` Ankita Garg
2010-08-19 18:58 ` Will Schmidt
2010-08-23 22:20 ` Darren Hart
2010-08-31 7:12 ` Darren Hart
2010-09-01 5:54 ` Michael Ellerman
2010-09-01 15:10 ` Darren Hart
2010-09-01 18:47 ` Darren Hart
2010-09-01 19:59 ` Steven Rostedt
2010-09-01 20:42 ` Darren Hart
2010-09-02 1:02 ` Michael Neuling
2010-09-02 4:06 ` Steven Rostedt
2010-09-02 6:04 ` Darren Hart
2010-09-03 20:10 ` Will Schmidt
2010-09-02 23:04 ` Michael Neuling
2010-09-03 0:08 ` Darren Hart
2010-09-02 3:46 ` Michael Neuling
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