LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Heinrich Schuchardt <xypron.glpk@gmx.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Aaron Tomlin <atomlin@redhat.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Davidlohr Bueso <dave@stgolabs.net>,
	David Rientjes <rientjes@google.com>,
	"David S. Miller" <davem@davemloft.net>,
	Fabian Frederick <fabf@skynet.be>,
	Guenter Roeck <linux@roeck-us.net>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
	Jens Axboe <axboe@fb.com>, Joe Perches <joe@perches.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Michael Marineau <mike@marineau.org>,
	Oleg Nesterov <oleg@redhat.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Prarit Bhargava <prarit@redhat.com>,
	Rik van Riel <riel@redhat.com>,
	Rusty Russell <rusty@rustcorp.com.au>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vladimir Davydov <vdavydov@parallels.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	Heinrich Schuchardt <xypron.glpk@gmx.de>
Subject: [PATCH 1/4 v6] kernel/fork.c: new function for max_threads
Date: Sun, 15 Mar 2015 17:13:35 +0100	[thread overview]
Message-ID: <1426436018-5159-2-git-send-email-xypron.glpk@gmx.de> (raw)
In-Reply-To: <1426436018-5159-1-git-send-email-xypron.glpk@gmx.de>

PAGE_SIZE is not guaranteed to be equal to or less than 8 times the
THREAD_SIZE.

E.g. architecture hexagon may have page size 1M and thread size 4096.
This would lead to a division by zero in the calculation of max_threads.

With this patch the buggy code is moved to a separate function
set_max_threads. The error is not fixed.

After fixing the problem in a separate patch the new function can be
reused to adjust max_threads after adding or removing memory.

Argument mempages of function fork_init() is removed as totalram_pages
is an exported symbol.

The creation of separate patches for refactoring to a new function
and for fixing the logic was suggested by Ingo Molnar.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
---
 init/main.c   |  4 ++--
 kernel/fork.c | 34 +++++++++++++++++++++-------------
 2 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/init/main.c b/init/main.c
index d4037ab..f470d14 100644
--- a/init/main.c
+++ b/init/main.c
@@ -93,7 +93,7 @@
 static int kernel_init(void *);
 
 extern void init_IRQ(void);
-extern void fork_init(unsigned long);
+extern void fork_init(void);
 extern void radix_tree_init(void);
 #ifndef CONFIG_DEBUG_RODATA
 static inline void mark_rodata_ro(void) { }
@@ -650,7 +650,7 @@ asmlinkage __visible void __init start_kernel(void)
 #endif
 	thread_info_cache_init();
 	cred_init();
-	fork_init(totalram_pages);
+	fork_init();
 	proc_caches_init();
 	buffer_init();
 	key_init();
diff --git a/kernel/fork.c b/kernel/fork.c
index 4dc2dda..bf1ff00 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -253,7 +253,26 @@ EXPORT_SYMBOL_GPL(__put_task_struct);
 
 void __init __weak arch_task_cache_init(void) { }
 
-void __init fork_init(unsigned long mempages)
+/*
+ * set_max_threads
+ */
+static void set_max_threads(void)
+{
+	/*
+	 * The default maximum number of threads is set to a safe
+	 * value: the thread structures can take up at most half
+	 * of memory.
+	 */
+	max_threads = totalram_pages / (8 * THREAD_SIZE / PAGE_SIZE);
+
+	/*
+	 * we need to allow at least 20 threads to boot a system
+	 */
+	if (max_threads < 20)
+		max_threads = 20;
+}
+
+void __init fork_init(void)
 {
 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 #ifndef ARCH_MIN_TASKALIGN
@@ -268,18 +287,7 @@ void __init fork_init(unsigned long mempages)
 	/* do the arch specific task caches init */
 	arch_task_cache_init();
 
-	/*
-	 * The default maximum number of threads is set to a safe
-	 * value: the thread structures can take up at most half
-	 * of memory.
-	 */
-	max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
-
-	/*
-	 * we need to allow at least 20 threads to boot a system
-	 */
-	if (max_threads < 20)
-		max_threads = 20;
+	set_max_threads();
 
 	init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
 	init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
-- 
2.1.4


  reply	other threads:[~2015-03-15 16:16 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-15 16:13 [PATCH 0/4 v6] max_threadx handling Heinrich Schuchardt
2015-03-15 16:13 ` Heinrich Schuchardt [this message]
2015-03-15 16:13 ` [PATCH 2/4 v6] kernel/fork.c: avoid division by zero Heinrich Schuchardt
2015-03-16  7:41   ` Ingo Molnar
2015-03-17 19:19     ` Heinrich Schuchardt
2015-03-18 16:49       ` Ingo Molnar
2015-03-18 17:06         ` Oleg Nesterov
2015-03-25 12:25           ` Ingo Molnar
2015-03-15 16:13 ` [PATCH 3/4 v6] kernel/sysctl.c: threads-max observe limits Heinrich Schuchardt
2015-03-15 16:13 ` [PATCH 4/4 v6] Doc/sysctl/kernel.txt: document threads-max Heinrich Schuchardt
2015-03-15 16:30   ` Guenter Roeck
2015-03-25 18:59 ` [PATCH 0/4 v6] max_threadx handling Heinrich Schuchardt

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1426436018-5159-2-git-send-email-xypron.glpk@gmx.de \
    --to=xypron.glpk@gmx.de \
    --cc=akpm@linux-foundation.org \
    --cc=atomlin@redhat.com \
    --cc=axboe@fb.com \
    --cc=corbet@lwn.net \
    --cc=dave@stgolabs.net \
    --cc=davem@davemloft.net \
    --cc=fabf@skynet.be \
    --cc=hannes@cmpxchg.org \
    --cc=hpa@zytor.com \
    --cc=joe@perches.com \
    --cc=keescook@chromium.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@roeck-us.net \
    --cc=luto@amacapital.net \
    --cc=mike@marineau.org \
    --cc=mingo@kernel.org \
    --cc=oleg@redhat.com \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peterz@infradead.org \
    --cc=prarit@redhat.com \
    --cc=riel@redhat.com \
    --cc=rientjes@google.com \
    --cc=rostedt@goodmis.org \
    --cc=rusty@rustcorp.com.au \
    --cc=tglx@linutronix.de \
    --cc=vdavydov@parallels.com \
    --subject='Re: [PATCH 1/4 v6] kernel/fork.c: new function for max_threads' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).