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Date: Tue, 10 May 2011 17:23:05 -0700 From: John Stultz <john.stultz@...aro.org> To: LKML <linux-kernel@...r.kernel.org> Cc: John Stultz <john.stultz@...aro.org>, "Ted Ts'o" <tytso@....edu>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, David Rientjes <rientjes@...gle.com>, Dave Hansen <dave@...ux.vnet.ibm.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org Subject: [PATCH 2/3] printk: Add %ptc to safely print a task's comm 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. Example use: printk("%ptc: unaligned epc - sending SIGBUS.\n", current); CC: Ted Ts'o <tytso@....edu> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> CC: David Rientjes <rientjes@...gle.com> CC: Dave Hansen <dave@...ux.vnet.ibm.com> CC: Andrew Morton <akpm@...ux-foundation.org> CC: linux-mm@...ck.org Signed-off-by: John Stultz <john.stultz@...aro.org> --- lib/vsprintf.c | 27 +++++++++++++++++++++++++++ 1 files changed, 27 insertions(+), 0 deletions(-) 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) +{ + struct task_struct *tsk = (struct task_struct *) addr; + 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)); + + return ret; +} + + + int kptr_restrict = 1; /* @@ -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); + } + break; case 'F': case 'f': ptr = dereference_function_descriptor(ptr); @@ -1151,6 +1177,7 @@ qualifier: * http://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-00 * %pU[bBlL] print a UUID/GUID in big or little endian using lower or upper * case. + * %ptc outputs the task's comm name * %n is ignored * * The return value is the number of characters which would -- 1.7.3.2.146.gca209 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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