Date: Thu, 19 Mar 2015 12:10:19 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Tiwei Bie <btw@mail.ustc.edu.cn> Cc: freebsd-hackers@freebsd.org, mjguzik@gmail.com Subject: Re: [PATCH] Finish the task 'Fix corefilename race' Message-ID: <20150319101019.GZ2379@kib.kiev.ua> In-Reply-To: <1426749223-18118-1-git-send-email-btw@mail.ustc.edu.cn> References: <1426749223-18118-1-git-send-email-btw@mail.ustc.edu.cn>
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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 ?
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.
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