linux-kernel - [PATCH 5.6 091/166] s390/cpum_sf: Fix wrong page count in error message

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Message-Id: <20200422095058.435527979@linuxfoundation.org>
Date:   Wed, 22 Apr 2020 11:56:58 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Richter <tmricht@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.6 091/166] s390/cpum_sf: Fix wrong page count in error message

From: Thomas Richter <tmricht@...ux.ibm.com>

[ Upstream commit 4141b6a5e9f171325effc36a22eb92bf961e7a5c ]

When perf record -e SF_CYCLES_BASIC_DIAG runs with very high
frequency, the samples arrive faster than the perf process can
save them to file. Eventually, for longer running processes, this
leads to the siutation where the trace buffers allocated by perf
slowly fills up. At one point the auxiliary trace buffer is full
and  the CPU Measurement sampling facility is turned off. Furthermore
a warning is printed to the kernel log buffer:

cpum_sf: The AUX buffer with 0 pages for the diagnostic-sampling
	mode is full

The number of allocated pages for the auxiliary trace buffer is shown
as zero pages. That is wrong.

Fix this by saving the number of allocated pages before entering the
work loop in the interrupt handler. When the interrupt handler processes
the samples, it may detect the buffer full condition and stop sampling,
reducing the buffer size to zero.
Print the correct value in the error message:

cpum_sf: The AUX buffer with 256 pages for the diagnostic-sampling
	mode is full

Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/s390/kernel/perf_cpum_sf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index b095b1c78987d..05b908b3a6b38 100644
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -1576,6 +1576,7 @@ static void hw_collect_aux(struct cpu_hw_sf *cpuhw)
 	unsigned long range = 0, size;
 	unsigned long long overflow = 0;
 	struct perf_output_handle *handle = &cpuhw->handle;
+	unsigned long num_sdb;
 
 	aux = perf_get_aux(handle);
 	if (WARN_ON_ONCE(!aux))
@@ -1587,13 +1588,14 @@ static void hw_collect_aux(struct cpu_hw_sf *cpuhw)
 			    size >> PAGE_SHIFT);
 	perf_aux_output_end(handle, size);
 
+	num_sdb = aux->sfb.num_sdb;
 	while (!done) {
 		/* Get an output handle */
 		aux = perf_aux_output_begin(handle, cpuhw->event);
 		if (handle->size == 0) {
 			pr_err("The AUX buffer with %lu pages for the "
 			       "diagnostic-sampling mode is full\n",
-				aux->sfb.num_sdb);
+				num_sdb);
 			debug_sprintf_event(sfdbg, 1,
 					    "%s: AUX buffer used up\n",
 					    __func__);
-- 
2.20.1