From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 381436B0011 for ; Tue, 10 May 2011 20:51:34 -0400 (EDT) Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm From: Joe Perches In-Reply-To: <1305073386-4810-3-git-send-email-john.stultz@linaro.org> References: <1305073386-4810-1-git-send-email-john.stultz@linaro.org> <1305073386-4810-3-git-send-email-john.stultz@linaro.org> Content-Type: text/plain; charset="UTF-8" Date: Tue, 10 May 2011 17:51:30 -0700 Message-ID: <1305075090.19586.189.camel@Joe-Laptop> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: John Stultz Cc: LKML , Ted Ts'o , KOSAKI Motohiro , David Rientjes , Dave Hansen , Andrew Morton , linux-mm@kvack.org On Tue, 2011-05-10 at 17:23 -0700, John Stultz wrote: > Acessing task->comm requires proper locking. However in the past > access to current->comm could be done without locking. This > is no longer the case, so all comm access needs to be done > while holding the comm_lock. > > In my attempt to clean up unprotected comm access, I've noticed > most comm access is done for printk output. To simpify correct > locking in these cases, I've introduced a new %ptc format, > which will safely print the corresponding task's comm. Hi John. Couple of tyops for Accessing and simplify in your commit message and a few comments on the patch. Could misuse of %ptc (not using current) cause system lockup? > Example use: > printk("%ptc: unaligned epc - sending SIGBUS.\n", current); > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index bc0ac6b..b9c97b8 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -797,6 +797,26 @@ char *uuid_string(char *buf, char *end, const u8 *addr, > return string(buf, end, uuid, spec); > } > > +static noinline_for_stack > +char *task_comm_string(char *buf, char *end, u8 *addr, > + struct printf_spec spec, const char *fmt) addr should be void * not u8 * > +{ > + struct task_struct *tsk = (struct task_struct *) addr; no cast. Maybe it'd be better to use current inside this routine and not pass the pointer at all. static noinline_for_stack char *task_comm_string(char *buf, char *end, struct printf_spec spec, const char *fmt) > + char *ret; > + unsigned long seq; > + > + do { > + seq = read_seqbegin(&tsk->comm_lock); > + > + ret = string(buf, end, tsk->comm, spec); > + > + } while (read_seqretry(&tsk->comm_lock, seq)); > @@ -864,6 +884,12 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, > } > > switch (*fmt) { > + case 't': > + switch (fmt[1]) { > + case 'c': > + return task_comm_string(buf, end, ptr, spec, fmt); maybe return task_comm_string(buf, end, spec, fmt); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org