Commits
Gu Zheng committed 3a41c5dbe8b
fb: reorder the lock sequence to fix potential dead lock
Following commits:
50e244cc79 fb: rework locking to fix lock ordering on takeover
e93a9a8687 fb: Yet another band-aid for fixing lockdep mess
054430e773 fbcon: fix locking harder
reworked locking to fix related lock ordering on takeover, and introduced console_lock
into fbmem, but it seems that the new lock sequence(fb_info->lock ---> console_lock)
is against with the one in console_callback(console_lock ---> fb_info->lock), and leads to
a potential dead lock as following:
[ 601.079000] ======================================================
[ 601.079000] [ INFO: possible circular locking dependency detected ]
[ 601.079000] 3.11.0 #189 Not tainted
[ 601.079000] -------------------------------------------------------
[ 601.079000] kworker/0:3/619 is trying to acquire lock:
[ 601.079000] (&fb_info->lock){+.+.+.}, at: [<ffffffff81397566>] lock_fb_info+0x26/0x60
[ 601.079000]
but task is already holding lock:
[ 601.079000] (console_lock){+.+.+.}, at: [<ffffffff8141aae3>] console_callback+0x13/0x160
[ 601.079000]
which lock already depends on the new lock.
[ 601.079000]
the existing dependency chain (in reverse order) is:
[ 601.079000]
-> #1 (console_lock){+.+.+.}:
[ 601.079000] [<ffffffff810dc971>] lock_acquire+0xa1/0x140
[ 601.079000] [<ffffffff810c6267>] console_lock+0x77/0x80
[ 601.079000] [<ffffffff81399448>] register_framebuffer+0x1d8/0x320
[ 601.079000] [<ffffffff81cfb4c8>] efifb_probe+0x408/0x48f
[ 601.079000] [<ffffffff8144a963>] platform_drv_probe+0x43/0x80
[ 601.079000] [<ffffffff8144853b>] driver_probe_device+0x8b/0x390
[ 601.079000] [<ffffffff814488eb>] __driver_attach+0xab/0xb0
[ 601.079000] [<ffffffff814463bd>] bus_for_each_dev+0x5d/0xa0
[ 601.079000] [<ffffffff81447e6e>] driver_attach+0x1e/0x20
[ 601.079000] [<ffffffff81447a07>] bus_add_driver+0x117/0x290
[ 601.079000] [<ffffffff81448fea>] driver_register+0x7a/0x170
[ 601.079000] [<ffffffff8144a10a>] __platform_driver_register+0x4a/0x50
[ 601.079000] [<ffffffff8144a12d>] platform_driver_probe+0x1d/0xb0
[ 601.079000] [<ffffffff81cfb0a1>] efifb_init+0x273/0x292
[ 601.079000] [<ffffffff81002132>] do_one_initcall+0x102/0x1c0
[ 601.079000] [<ffffffff81cb80a6>] kernel_init_freeable+0x15d/0x1ef
[ 601.079000] [<ffffffff8166d2de>] kernel_init+0xe/0xf0
[ 601.079000] [<ffffffff816914ec>] ret_from_fork+0x7c/0xb0
[ 601.079000]
-> #0 (&fb_info->lock){+.+.+.}:
[ 601.079000] [<ffffffff810dc1d8>] __lock_acquire+0x1e18/0x1f10
[ 601.079000] [<ffffffff810dc971>] lock_acquire+0xa1/0x140
[ 601.079000] [<ffffffff816835ca>] mutex_lock_nested+0x7a/0x3b0
[ 601.079000] [<ffffffff81397566>] lock_fb_info+0x26/0x60
[ 601.079000] [<ffffffff813a4aeb>] fbcon_blank+0x29b/0x2e0
[ 601.079000] [<ffffffff81418658>] do_blank_screen+0x1d8/0x280
[ 601.079000] [<ffffffff8141ab34>] console_callback+0x64/0x160
[ 601.079000] [<ffffffff8108d855>] process_one_work+0x1f5/0x540
[ 601.079000] [<ffffffff8108e04c>] worker_thread+0x11c/0x370
[ 601.079000] [<ffffffff81095fbd>] kthread+0xed/0x100
[ 601.079000] [<ffffffff816914ec>] ret_from_fork+0x7c/0xb0
[ 601.079000]
other info that might help us debug this:
[ 601.079000] Possible unsafe locking scenario:
[ 601.079000] CPU0 CPU1
[ 601.079000] ---- ----
[ 601.079000] lock(console_lock);
[ 601.079000] lock(&fb_info->lock);
[ 601.079000] lock(console_lock);
[ 601.079000] lock(&fb_info->lock);
[ 601.079000]
*** DEADLOCK ***
so we reorder the lock sequence the same as it in console_callback() to
avoid this issue. And following Tomi's suggestion, fix these similar
issues all in fb subsystem.
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>