linux-kernel - [tip:perfcounters/core] perf_counter: Fix lockup with interrupting counters

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <tip-6dc5f2a41759987e35e757ef00192e7b424563bb@git.kernel.org>
Date:	Fri, 5 Jun 2009 06:24:45 GMT
From:	tip-bot for Paul Mackerras <paulus@...ba.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:perfcounters/core] perf_counter: Fix lockup with interrupting counters

Commit-ID:  6dc5f2a41759987e35e757ef00192e7b424563bb
Gitweb:     http://git.kernel.org/tip/6dc5f2a41759987e35e757ef00192e7b424563bb
Author:     Paul Mackerras <paulus@...ba.org>
AuthorDate: Fri, 5 Jun 2009 12:36:28 +1000
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 5 Jun 2009 08:22:26 +0200

perf_counter: Fix lockup with interrupting counters

Commit 8e3747c1 ("perf_counter: Change data head from u32 to u64")
changed the type of 'head' in struct perf_mmap_data from atomic_t
to atomic_long_t, but missed converting one use of atomic_read on
it to atomic_long_read.  The effect of using atomic_read rather than
atomic_long_read on powerpc (and other big-endian architectures) is
that we get the high half of the 64-bit quantity, resulting in the
cmpxchg retry loop in perf_output_begin spinning forever as soon as
data->head becomes non-zero.  On little-endian architectures such as
x86 we would get the low half, resulting in a lockup once data->head
becomes greater than 4G.

This fixes it by using atomic_long_read rather than atomic_read.

[ Impact: fix perfcounter lockup on PowerPC / big-endian systems ]

Signed-off-by: Paul Mackerras <paulus@...ba.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <18984.33964.21541.743096@...go.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 kernel/perf_counter.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 195712e..a5d3e2a 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -2234,7 +2234,7 @@ static int perf_output_begin(struct perf_output_handle *handle,
 	perf_output_lock(handle);
 
 	do {
-		offset = head = atomic_read(&data->head);
+		offset = head = atomic_long_read(&data->head);
 		head += size;
 	} while (atomic_long_cmpxchg(&data->head, offset, head) != offset);
 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/