Commit c240837f authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

signals: jffs2: fix the wrong usage of disallow_signal() 



jffs2_garbage_collect_thread() does disallow_signal(SIGHUP) around
jffs2_garbage_collect_pass() and the comment says "We don't want SIGHUP
to interrupt us".

But disallow_signal() can't ensure that jffs2_garbage_collect_pass()
won't be interrupted by SIGHUP, the problem is that SIGHUP can be
already pending when disallow_signal() is called, and in this case any
interruptible sleep won't block.

Note: this is in fact because disallow_signal() is buggy and should be
fixed, see the next changes.

But there is another reason why disallow_signal() is wrong: SIG_IGN set
by disallow_signal() silently discards any SIGHUP which can be sent
before the next allow_signal(SIGHUP).

Change this code to use sigprocmask(SIG_UNBLOCK/SIG_BLOCK, SIGHUP).
This even matches the old (and wrong) semantics allow/disallow had when
this logic was written.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0341729b

fs/jffs2/background.c

+7 −5
Original line number Original line Diff line number Diff line
@@ -75,10 +75,13 @@ void jffs2_stop_garbage_collect_thread(struct jffs2_sb_info *c) 
static int jffs2_garbage_collect_thread(void *_c)

static int jffs2_garbage_collect_thread(void *_c)

{

{

	struct jffs2_sb_info *c = _c;

	struct jffs2_sb_info *c = _c;

	sigset_t hupmask;





	siginitset(&hupmask, sigmask(SIGHUP));

	allow_signal(SIGKILL);

	allow_signal(SIGKILL);

	allow_signal(SIGSTOP);

	allow_signal(SIGSTOP);

	allow_signal(SIGCONT);

	allow_signal(SIGCONT);

	allow_signal(SIGHUP);





	c->gc_task = current;

	c->gc_task = current;

	complete(&c->gc_thread_start);

	complete(&c->gc_thread_start);
@@ -87,7 +90,7 @@ static int jffs2_garbage_collect_thread(void *_c) 




	set_freezable();

	set_freezable();

	for (;;) {

	for (;;) {

		allow_signal(SIGHUP);

		sigprocmask(SIG_UNBLOCK, &hupmask, NULL);

	again:

	again:

		spin_lock(&c->erase_completion_lock);

		spin_lock(&c->erase_completion_lock);

		if (!jffs2_thread_should_wake(c)) {

		if (!jffs2_thread_should_wake(c)) {
@@ -95,10 +98,9 @@ static int jffs2_garbage_collect_thread(void *_c) 
			spin_unlock(&c->erase_completion_lock);

			spin_unlock(&c->erase_completion_lock);

			jffs2_dbg(1, "%s(): sleeping...\n", __func__);

			jffs2_dbg(1, "%s(): sleeping...\n", __func__);

			schedule();

			schedule();

		} else

		} else {

			spin_unlock(&c->erase_completion_lock);

			spin_unlock(&c->erase_completion_lock);

			

		}



		/* Problem - immediately after bootup, the GCD spends a lot

		/* Problem - immediately after bootup, the GCD spends a lot

		 * of time in places like jffs2_kill_fragtree(); so much so

		 * of time in places like jffs2_kill_fragtree(); so much so

		 * that userspace processes (like gdm and X) are starved

		 * that userspace processes (like gdm and X) are starved
@@ -150,7 +152,7 @@ static int jffs2_garbage_collect_thread(void *_c) 
			}

			}

		}

		}

		/* We don't want SIGHUP to interrupt us. STOP and KILL are OK though. */

		/* We don't want SIGHUP to interrupt us. STOP and KILL are OK though. */

		disallow_signal(SIGHUP);

		sigprocmask(SIG_BLOCK, &hupmask, NULL);





		jffs2_dbg(1, "%s(): pass\n", __func__);

		jffs2_dbg(1, "%s(): pass\n", __func__);

		if (jffs2_garbage_collect_pass(c) == -ENOSPC) {

		if (jffs2_garbage_collect_pass(c) == -ENOSPC) {

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