Re: [PATCH] Revert "perf: Fix perf_event_validate_size()"
From: Mark Rutland
Date: Thu Dec 14 2023 - 10:13:08 EST
On Wed, Dec 13, 2023 at 04:06:20PM -0800, Lucas De Marchi wrote:
> This reverts commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b.
>
> When using for_each_sibling_event() lockdep complains on
>
> WARN_ON_ONCE(__lockdep_enabled && \
> (this_cpu_read(hardirqs_enabled) && \
> lockdep_is_held(&(event)->ctx->mutex) != LOCK_STATE_HELD))
>
> after a simple `perf stat -e instructions sleep 1`:
>
> WARNING: CPU: 8 PID: 1471 at kernel/events/core.c:1950 __do_sys_perf_event_open+0xf37/0x1080
> Modules linked in: x86_pkg_temp_thermal coretemp kvm_intel kvm e1000e igc irqbypass mei_pxp mei_hdcp crct10dif_pclmul wmi_bmof crc32_pclmul ghash_clmulni_intel i2c_i801 ptp mei_me i2c_smbus pps_core mei intel_lpss_pci video wmi fuse
> CPU: 8 PID: 1471 Comm: perf Not tainted 6.7.0-rc5-linus-demarchi+ #8
> Hardware name: Intel Corporation Rocket Lake Client Platform/RocketLake S UDIMM 4L ERB, BIOS RKLSFWI1.R00.2022.A00.2101052151 01/05/2021
> RIP: 0010:__do_sys_perf_event_open+0xf37/0x1080
> Code: ff e8 ed 30 ab 00 48 8b 81 28 02 00 00 83 ce ff 48 8d b8 a8 00 00 00 e8 67 38 ab 00 48 8b 4c 24 08 83 e8 01 0f 84 56 f9 ff ff <0f> 0b e9 4f f9 ff ff be 03 00 00 00 e8 d8 74 40 00 e9 54 fa ff ff
> RSP: 0018:ffffc90001d6be40 EFLAGS: 00010297
> RAX: 00000000ffffffff RBX: ffff888112bc8040 RCX: ffff888100c34568
> RDX: 0000000080000000 RSI: ffffffff823e2806 RDI: ffffffff824023cb
> RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
> R10: 0000000000000001 R11: 0000000000000000 R12: ffff888106560800
> R13: 0000000000000000 R14: 0000000000080002 R15: ffff888100c34568
> FS: 00007f723d196c00(0000) GS:ffff888450800000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005624c0efdaa0 CR3: 00000001199de002 CR4: 0000000000770ef0
> PKRU: 55555554
> Call Trace:
> <TASK>
> ? __do_sys_perf_event_open+0xf37/0x1080
> ? __warn+0x80/0x170
> ? __do_sys_perf_event_open+0xf37/0x1080
> ? report_bug+0x191/0x1c0
> ? handle_bug+0x3c/0x70
> ? exc_invalid_op+0x17/0x70
> ? asm_exc_invalid_op+0x1a/0x20
> ? __do_sys_perf_event_open+0xf37/0x1080
> do_syscall_64+0x42/0xf0
> entry_SYSCALL_64_after_hwframe+0x6e/0x76
> RIP: 0033:0x7f723bf1ea7d
> Code: 5b 41 5c c3 66 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 83 a3 0f 00 f7 d8 64 89 01 48
> RSP: 002b:00007ffc7118ba68 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
> RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 00007f723bf1ea7d
> RDX: 00000000ffffffff RSI: 00000000000005c0 RDI: 00005624c0efb0c0
> RBP: 00007ffc7118bb20 R08: 0000000000000008 R09: 0000000000000000
> R10: 00000000ffffffff R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000008 R14: 00005624c0efb0b0 R15: 00005624c0efb0b0
> </TASK>
> irq event stamp: 45697
> hardirqs last enabled at (45703): [<ffffffff81173dca>] console_unlock+0x10a/0x160
> hardirqs last disabled at (45708): [<ffffffff81173daf>] console_unlock+0xef/0x160
> softirqs last enabled at (45276): [<ffffffff810dab0e>] irq_exit_rcu+0x8e/0xf0
> softirqs last disabled at (45267): [<ffffffff810dab0e>] irq_exit_rcu+0x8e/0xf0
>
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/9847
> Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
> ---
>
> Not sure about a proper fix for this. At first I thought it was indeed
> because previously it was not validating the the size correctly. However
> then I noticed the warning is actually due to for_each_sibling_event().
I think what's happening here is that at the point we call
perf_event_validate_size(), we've found and locked the relevant
perf_event_context, but haven't set event->ctx yet via
perf_install_in_context().
Thanks to earlier checks, we know that group_leader->ctx == ctx, so we have
actually locked the relevant context, but for_each_sibling_event() doesn't have
access to the context to discover that.
The diff below worked for me, though it's a bit ugly.
Peter, thoughts?
Mark.
---->8----
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 5547ba68e6e4..c1e625cef6ca 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -652,19 +652,22 @@ struct pmu_event_list {
* disabled is sufficient since it will hold-off the IPIs.
*/
#ifdef CONFIG_PROVE_LOCKING
-#define lockdep_assert_event_ctx(event) \
+#define lockdep_assert_event_ctx(ctx) \
WARN_ON_ONCE(__lockdep_enabled && \
(this_cpu_read(hardirqs_enabled) && \
- lockdep_is_held(&(event)->ctx->mutex) != LOCK_STATE_HELD))
+ lockdep_is_held(&(ctx)->mutex) != LOCK_STATE_HELD))
#else
#define lockdep_assert_event_ctx(event)
#endif
-#define for_each_sibling_event(sibling, event) \
- lockdep_assert_event_ctx(event); \
+#define for_each_sibling_event_ctx(sibling, event, ctx) \
+ lockdep_assert_event_ctx(ctx); \
if ((event)->group_leader == (event)) \
list_for_each_entry((sibling), &(event)->sibling_list, sibling_list)
+#define for_each_sibling_event(sibling, event) \
+ for_each_sibling_event_ctx(sibling, event, event->ctx)
+
/**
* struct perf_event - performance event kernel representation:
*/
diff --git a/kernel/events/core.c b/kernel/events/core.c
index c9d123e13b57..2745de6c4faf 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1935,7 +1935,8 @@ static void perf_event__id_header_size(struct perf_event *event)
* This leaves 48k for the constant size fields and things like callchains,
* branch stacks and register sets.
*/
-static bool perf_event_validate_size(struct perf_event *event)
+static bool perf_event_validate_size(struct perf_event *event,
+ struct perf_event_context *ctx)
{
struct perf_event *sibling, *group_leader = event->group_leader;
@@ -1947,7 +1948,7 @@ static bool perf_event_validate_size(struct perf_event *event)
group_leader->nr_siblings + 1) > 16*1024)
return false;
- for_each_sibling_event(sibling, group_leader) {
+ for_each_sibling_event_ctx(sibling, group_leader, ctx) {
if (__perf_event_read_size(sibling->attr.read_format,
group_leader->nr_siblings + 1) > 16*1024)
return false;
@@ -12652,7 +12653,7 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_context;
}
- if (!perf_event_validate_size(event)) {
+ if (!perf_event_validate_size(event, ctx)) {
err = -E2BIG;
goto err_context;
}