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Fri, 15 Nov 2024 11:36:15 GMT Received: from pps.reinject (localhost [127.0.0.1]) by phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTPS id 42sx6c38cf-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 15 Nov 2024 11:36:15 +0000 Received: from phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 4AFBa9PJ010008; Fri, 15 Nov 2024 11:36:15 GMT Received: from bpf.uk.oracle.com (dhcp-10-175-214-128.vpn.oracle.com [10.175.214.128]) by phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTP id 42sx6c388q-3; Fri, 15 Nov 2024 11:36:15 +0000 From: Alan Maguire To: acme@kernel.org Cc: yonghong.song@linux.dev, dwarves@vger.kernel.org, ast@kernel.org, andrii@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, kernel-team@fb.com, song@kernel.org, eddyz87@gmail.com, olsajiri@gmail.com, Alan Maguire , Jiri Olsa Subject: [PATCH v3 dwarves 2/2] dwarf_loader: use libdw__lock for dwarf_getlocation(s) Date: Fri, 15 Nov 2024 11:36:05 +0000 Message-ID: <20241115113605.1504796-3-alan.maguire@oracle.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20241115113605.1504796-1-alan.maguire@oracle.com> References: <20241115113605.1504796-1-alan.maguire@oracle.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-11-14_05,2024-11-14_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 malwarescore=0 mlxscore=0 bulkscore=0 suspectscore=0 phishscore=0 mlxlogscore=954 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2409260000 definitions=main-2411150099 X-Proofpoint-ORIG-GUID: tTOA5QEKDXJ2a4K1sJ_JJD1DzsAvFq7Y X-Proofpoint-GUID: tTOA5QEKDXJ2a4K1sJ_JJD1DzsAvFq7Y Eduard noticed [1] intermittent segmentation faults triggered by caching done internally in dwarf_getlocation(s). A binary tree of location information is cached in the CU, and if multiple threads access it concurrently we can get segmentation faults. It is possible to compile elfutils with experimental thread-safe support, but safer for now to add locking to pahole. No additional overhead in pahole encoding was observed as a result of these changes. Reported-by: Eduard Zingerman Suggested-by: Arnaldo Carvalho de Melo Signed-off-by: Alan Maguire Acked-by: Eduard Zingerman Acked-by: Jiri Olsa [1] https://lore.kernel.org/dwarves/080794545d8eb3df3d6eba90ac621111ab7171f5.camel@gmail.com/ --- dwarf_loader.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/dwarf_loader.c b/dwarf_loader.c index 4789967..598fde4 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -450,7 +450,14 @@ static bool attr_type(Dwarf_Die *die, uint32_t attr_name, Dwarf_Off *offset) static int attr_location(Dwarf_Die *die, Dwarf_Op **expr, size_t *exprlen) { Dwarf_Attribute attr; + int ret = 1; + if (dwarf_attr(die, DW_AT_location, &attr) != NULL) { + /* use libdw__lock as dwarf_getlocation(s) has concurrency + * issues when libdw is not compiled with experimental + * --enable-thread-safety + */ + pthread_mutex_lock(&libdw__lock); if (dwarf_getlocation(&attr, expr, exprlen) == 0) { /* DW_OP_addrx needs additional lookup for real addr. */ if (*exprlen != 0 && expr[0]->atom == DW_OP_addrx) { @@ -462,11 +469,12 @@ static int attr_location(Dwarf_Die *die, Dwarf_Op **expr, size_t *exprlen) expr[0]->number = address; } - return 0; + ret = 0; } + pthread_mutex_unlock(&libdw__lock); } - return 1; + return ret; } /* The struct dwarf_tag has a fixed size while the 'struct tag' is just the base @@ -1194,6 +1202,10 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg) int loc_num = -1; int ret = -1; + /* use libdw__lock as dwarf_getlocation(s) has concurrency issues + * when libdw is not compiled with experimental --enable-thread-safety + */ + pthread_mutex_lock(&libdw__lock); while ((offset = __dwarf_getlocations(attr, offset, &base, &start, &end, &expr, &exprlen)) > 0) { loc_num++; @@ -1230,6 +1242,7 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg) } } out: + pthread_mutex_unlock(&libdw__lock); return ret; }