Commit 8dab6376 authored Jan 11, 2008 by Jeremy Kerr Committed by Linus Torvalds Jan 11, 2008

ps3fb: fix deadlock on kexec()



Since the introduction of the acquire_console_sem calls in
0333d835, kexecing can cause the
kernel to deadlock:

 ps3fb_shutdown()
  -> unregister_framebuffer()
  -> fb_notifier_call_chain(FB_EVENT_FB_UNBIND)
  -> fbcon_fb_unbind()
  -> unbind_con_driver()
  -> bind_con_driver()
	[ acquires console_sem ]
  -> fbcon_deinit()
  -> fbops->fb_release(newinfo, 0)
  -> ps3fb_release()
  -> ps3fb_sync()
	[ acquires console_sem ]

This change avoids the deadlock by moving the acquire_console_sem()
out of ps3fb_sync(), and puts it into the two other callsites, leaving
ps3fb_release() to call ps3fb_sync() without the console semaphore.

[Geert]
  - Corrected call sequence above
  - ps3fb_release() may be called with and without console_sem held. This is an
    inconsistency that should be fixed at the fb level, but for now, try to
    acquire console_sem in ps3fb_release().

    I think it's safer to let ps3fb_release() try to acquire console_sem and
    not refresh the screen if it fails, than to call ps3fb_sync() without
    holding console_sem, as ps3fb_par may be modified at the same time, causing
    crashes or lockups.

    Besides, ps3fb_release() only calls ps3fb_sync() to refresh the screen
    when display flipping is disabled, which is an uncommon case (except during
    shutdown/kexec).

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ba21611c

drivers/video/ps3fb.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -443,8 +443,6 @@ static int ps3fb_sync(struct fb_info *info, u32 frame)
		u32 ddr_line_length, xdr_line_length;
		u64 ddr_base, xdr_base;

		acquire_console_sem();

		if (frame > par->num_frames - 1) {
		dev_dbg(info->device, "%s: invalid frame number (%u)\n",
		__func__, frame);
		@@ -464,7 +462,6 @@ static int ps3fb_sync(struct fb_info *info, u32 frame)
		xdr_line_length);

		out:
		release_console_sem();
		return error;
		}

		@@ -479,7 +476,10 @@ static int ps3fb_release(struct fb_info *info, int user)
		if (atomic_dec_and_test(&ps3fb.f_count)) {
		if (atomic_read(&ps3fb.ext_flip)) {
		atomic_set(&ps3fb.ext_flip, 0);
		if (!try_acquire_console_sem()) {
		ps3fb_sync(info, 0); /* single buffer */
		release_console_sem();
		}
		}
		}
		return 0;
		@@ -865,7 +865,9 @@ static int ps3fb_ioctl(struct fb_info *info, unsigned int cmd,
		break;

		dev_dbg(info->device, "PS3FB_IOCTL_FSEL:%d\n", val);
		acquire_console_sem();
		retval = ps3fb_sync(info, val);
		release_console_sem();
		break;

		default:
		@@ -885,7 +887,9 @@ static int ps3fbd(void *arg)
		set_current_state(TASK_INTERRUPTIBLE);
		if (ps3fb.is_kicked) {
		ps3fb.is_kicked = 0;
		acquire_console_sem();
		ps3fb_sync(info, 0); /* single buffer */
		release_console_sem();
		}
		schedule();
		}

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