From owner-freebsd-hackers@FreeBSD.ORG Thu Mar 19 11:35:55 2015 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 2633635C for ; Thu, 19 Mar 2015 11:35:55 +0000 (UTC) Received: from ustc.edu.cn (email6.ustc.edu.cn [IPv6:2001:da8:d800::8]) by mx1.freebsd.org (Postfix) with ESMTP id 4918E1EC for ; Thu, 19 Mar 2015 11:35:53 +0000 (UTC) Received: from freebsd (unknown [58.211.218.74]) by newmailweb.ustc.edu.cn (Coremail) with SMTP id LkAmygAXHiqQtApV2a2yAw--.32939S2; Thu, 19 Mar 2015 19:35:49 +0800 (CST) Date: Thu, 19 Mar 2015 19:35:30 +0800 From: Tiwei Bie To: Konstantin Belousov Subject: Re: [PATCH] Finish the task 'Fix corefilename race' Message-ID: <20150319113530.GA33176@freebsd> References: <1426749223-18118-1-git-send-email-btw@mail.ustc.edu.cn> <20150319101019.GZ2379@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150319101019.GZ2379@kib.kiev.ua> User-Agent: Mutt/1.5.23 (2014-03-12) X-CM-TRANSID: LkAmygAXHiqQtApV2a2yAw--.32939S2 X-Coremail-Antispam: 1UD129KBjvJXoWxZr13KFWkAFWrGr1kZF17trb_yoWrZFyUpF sYk3yrArs5CF45CFn3Za15CF1Yyw18tr4jg345XF4YyrnYvrykXF1rKryFgF1kWrn2g34D ta15Xr9xKryjqaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkYb7Iv0xC_Kw4lb4IE77IF4wAFF20E14v26r1j6r4UM7CY07I2 0VC2zVCF04k26cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rw A2F7IY1VAKz4vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Ar0_tr1l84ACjcxK6xII jxv20xvEc7CjxVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwV C2z280aVCY1x0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC 0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Cr0_Gr 1UMcvjeVCFs4IE7xkEbVWUJVW8JwACjcxG0xvEwIxGrwCY02Avz4vE14v_Gw4l42xK82IY c2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s 026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1Y6r17MIIYrxkI7VAKI48JMIIF 0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r1j6r4UMIIF0x vE42xK8VAvwI8IcIk0rVWrZr1j6s0DMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2 jsIEc7CjxVAFwI0_Jr0_GrUvcSsGvfC2KfnxnUUI43ZEXa7IU5m0PPUUUUU== X-CM-SenderInfo: xewzqzxdloh3xvwfhvlgxou0/1tbiAQUNAVQhl-l6PQALsf Cc: freebsd-hackers@freebsd.org, mjguzik@gmail.com X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 19 Mar 2015 11:35:55 -0000 On Thu, Mar 19, 2015 at 12:10:19PM +0200, Konstantin Belousov wrote: > On Thu, Mar 19, 2015 at 03:13:43PM +0800, Tiwei Bie wrote: > > Hi, Mateusz! > > > > I have finished the task: Fix corefilename race [1]. > > > > Following is my patch: > > > > --- > > sys/kern/kern_sig.c | 22 ++++++++++++++++++++-- > > 1 file changed, 20 insertions(+), 2 deletions(-) > > > > diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c > > index 58d9707..a1421cb 100644 > > --- a/sys/kern/kern_sig.c > > +++ b/sys/kern/kern_sig.c > > @@ -3090,8 +3090,24 @@ static int compress_user_cores = 0; > > #endif > > > > static char corefilename[MAXPATHLEN] = {"%N.core"}; > > -SYSCTL_STRING(_kern, OID_AUTO, corefile, CTLFLAG_RWTUN, corefilename, > > - sizeof(corefilename), "Process corefile name format string"); > > + > > +static struct sx corefilename_lock; > > +SX_SYSINIT(corefilename_init, &corefilename_lock, "corefilename lock"); > > + > > +static int > > +sysctl_kern_corefile(SYSCTL_HANDLER_ARGS) > > +{ > > + int error; > > + > > + sx_xlock(&corefilename_lock); > > + error = sysctl_handle_string(oidp, corefilename, MAXPATHLEN, req); > > + sx_xunlock(&corefilename_lock); > > + > > + return (error); > > +} > > +SYSCTL_PROC(_kern, OID_AUTO, corefile, CTLTYPE_STRING | CTLFLAG_RWTUN | > > + CTLFLAG_MPSAFE, 0, 0, sysctl_kern_corefile, "A", > > + "Process corefile name format string"); > > > > /* > > * corefile_open(comm, uid, pid, td, compress, vpp, namep) > > @@ -3120,6 +3136,7 @@ corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td, > > name = malloc(MAXPATHLEN, M_TEMP, M_WAITOK | M_ZERO); > > indexpos = -1; > > (void)sbuf_new(&sb, name, MAXPATHLEN, SBUF_FIXEDLEN); > > + sx_slock(&corefilename_lock); > > for (i = 0; format[i] != '\0'; i++) { > > switch (format[i]) { > > case '%': /* Format character */ > > @@ -3162,6 +3179,7 @@ corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td, > > break; > > } > > } > > + sx_sunlock(&corefilename_lock); > > free(hostname, M_TEMP); > > if (compress) > > sbuf_printf(&sb, GZ_SUFFIX); > > So the race is between somebody setting the core path string and another > process coredumping, am I right ? > Yeah, you are right! > If you, could you try to reuse some existing lock for the task ? It is a > waste to have sx dedicated to the task, which is probably never used by > 99% of the machines in the world. Yeah, of course. After a quick `grep'ing, I found the sx lock: allprison_lock, which is defined in kern/kern_jail.c. It is rarely acquired as an exclusive lock, and is not defined as a static variable. So I think it will be a good candidate for this task. Here is my new patch: --- sys/kern/kern_sig.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c index 58d9707..cc99f8f 100644 --- a/sys/kern/kern_sig.c +++ b/sys/kern/kern_sig.c @@ -3089,9 +3089,24 @@ SYSCTL_INT(_kern, OID_AUTO, compress_user_cores_gzlevel, CTLFLAG_RWTUN, static int compress_user_cores = 0; #endif +#define corefilename_lock allprison_lock + static char corefilename[MAXPATHLEN] = {"%N.core"}; -SYSCTL_STRING(_kern, OID_AUTO, corefile, CTLFLAG_RWTUN, corefilename, - sizeof(corefilename), "Process corefile name format string"); + +static int +sysctl_kern_corefile(SYSCTL_HANDLER_ARGS) +{ + int error; + + sx_xlock(&corefilename_lock); + error = sysctl_handle_string(oidp, corefilename, MAXPATHLEN, req); + sx_xunlock(&corefilename_lock); + + return (error); +} +SYSCTL_PROC(_kern, OID_AUTO, corefile, CTLTYPE_STRING | CTLFLAG_RWTUN | + CTLFLAG_MPSAFE, 0, 0, sysctl_kern_corefile, "A", + "Process corefile name format string"); /* * corefile_open(comm, uid, pid, td, compress, vpp, namep) @@ -3120,6 +3135,7 @@ corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td, name = malloc(MAXPATHLEN, M_TEMP, M_WAITOK | M_ZERO); indexpos = -1; (void)sbuf_new(&sb, name, MAXPATHLEN, SBUF_FIXEDLEN); + sx_slock(&corefilename_lock); for (i = 0; format[i] != '\0'; i++) { switch (format[i]) { case '%': /* Format character */ @@ -3162,6 +3178,7 @@ corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td, break; } } + sx_sunlock(&corefilename_lock); free(hostname, M_TEMP); if (compress) sbuf_printf(&sb, GZ_SUFFIX); -- 2.1.2 Best regards, Tiwei Bie