[PATCH 1/2] trace: disable preemption before taking raw spinlocks

From: Frederic Weisbecker
Date: Wed May 27 2009 - 19:35:57 EST

From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>

s390 code uses smp_processor_id() in __raw_spin_lock() code which
reveals that a (raw) spinlock is taken without preemption disabled.
This can potentially deadlock.

To fix this explicitly disable and enable preemption.

BUG: using smp_processor_id() in preemptible [00000000] code: cat/2278
caller is trace_find_cmdline+0x40/0xfc
CPU: 0 Not tainted 2.6.30-rc7-dirty #39
Process cat (pid: 2278, task: 000000003faedb68, ksp: 000000003b33b988)
000000003b33b988 000000003b33bae0 0000000000000002 0000000000000000
000000003b33bb80 000000003b33baf8 000000003b33baf8 00000000000175d6
0000000000000001 000000003b33b988 000000003f9b0000 000000000000000b
000000000000000c 000000003b33bb40 000000003b33bae0 0000000000000000
0000000000000000 00000000000175d6 000000003b33bae0 000000003b33bb28
Call Trace:
([<00000000000174b2>] show_trace+0x112/0x170)
[<0000000000017582>] show_stack+0x72/0x100
[<0000000000441538>] dump_stack+0xc8/0xd8
[<000000000025c350>] debug_smp_processor_id+0x114/0x130
[<00000000000bf0e4>] trace_find_cmdline+0x40/0xfc
[<00000000000c35d4>] trace_print_context+0x58/0xac
[<00000000000bb676>] print_trace_line+0x416/0x470
[<00000000000bc8fe>] s_show+0x4e/0x428
[<000000000013834e>] seq_read+0x36a/0x5d4
[<0000000000112a78>] vfs_read+0xc8/0x174
[<0000000000112c58>] SyS_read+0x74/0xc4
[<000000000002c7ae>] sysc_noemu+0x10/0x16
[<000002000012436c>] 0x2000012436c
1 lock held by cat/2278:
#0: (&p->lock){+.+.+.}, at: [<0000000000138056>] seq_read+0x72/0x5d4

[ Impact: fix preempt-unsafe raw spinlock ]

Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
kernel/trace/trace.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 02d32ba..a3a8a87 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -808,6 +808,7 @@ void trace_find_cmdline(int pid, char comm[])

+ preempt_disable();
map = map_pid_to_cmdline[pid];
if (map != NO_CMDLINE_MAP)
@@ -816,6 +817,7 @@ void trace_find_cmdline(int pid, char comm[])
strcpy(comm, "<...>");

+ preempt_enable();

void tracing_record_cmdline(struct task_struct *tsk)

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