From: Andrey Ryabinin <aryabinin@odin.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Tejun Heo <tj@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Dmitry Vyukov <dvyukov@google.com>,
Sasha Levin <sasha.levin@oracle.com>
Subject: undefined shift in wb_update_dirty_ratelimit()
Date: Mon, 7 Dec 2015 17:17:06 +0300 [thread overview]
Message-ID: <566594E2.3050306@odin.com> (raw)
I've hit undefined shift in wb_update_dirty_ratelimit() which does some
mysterious 'step' calculations:
/*
* Don't pursue 100% rate matching. It's impossible since the balanced
* rate itself is constantly fluctuating. So decrease the track speed
* when it gets close to the target. Helps eliminate pointless tremors.
*/
step >>= dirty_ratelimit / (2 * step + 1);
dirty_ratelimit = INIT_BW and step = 0 results in this:
[ 5006.957366] ================================================================================
[ 5006.957798] UBSAN: Undefined behaviour in ../mm/page-writeback.c:1286:7
[ 5006.958091] shift exponent 25600 is too large for 64-bit type 'long unsigned int'
[ 5006.958414] CPU: 2 PID: 7452 Comm: trinity-c2 Not tainted 4.4.0-rc1+ #19
[ 5006.958740] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
[ 5006.959247] ffffffff8261427a ffff88007ddaf798 ffffffff815e6cd6 0000000000000001
[ 5006.959630] ffff88007ddaf7c8 ffff88007ddaf7b0 ffffffff8163a62d ffffffff8261427a
[ 5006.959997] ffff88007ddaf850 ffffffff8163accf ffff88013afac780 0000000000000202
[ 5006.960345] Call Trace:
[ 5006.960460] [<ffffffff815e6cd6>] dump_stack+0x45/0x5f
[ 5006.960723] [<ffffffff8163a62d>] ubsan_epilogue+0xd/0x40
[ 5006.960961] [<ffffffff8163accf>] __ubsan_handle_shift_out_of_bounds+0xef/0x130
[ 5006.961282] [<ffffffff8140555c>] ? __es_insert_extent+0x2ec/0x670
[ 5006.961554] [<ffffffff815f19f3>] ? radix_tree_lookup_slot+0x13/0x30
[ 5006.961867] [<ffffffff81218431>] __wb_update_bandwidth.constprop.26+0x521/0x6a0
[ 5006.962190] [<ffffffff81219c67>] balance_dirty_pages.isra.23+0xa27/0x1900
[ 5006.962498] [<ffffffff814174b7>] ? jbd2_journal_stop+0x237/0x6b0
[ 5006.962835] [<ffffffff81301d1f>] ? __block_commit_write.isra.23+0x6f/0x140
[ 5006.963140] [<ffffffff8121aca3>] balance_dirty_pages_ratelimited+0x163/0x340
[ 5006.963453] [<ffffffff81204954>] generic_perform_write+0x184/0x290
[ 5006.963750] [<ffffffff81206bb7>] __generic_file_write_iter+0x1b7/0x3b0
[ 5006.964064] [<ffffffff8137fdc4>] ext4_file_write_iter+0x154/0x930
[ 5006.964336] [<ffffffff812ad414>] vfs_iter_write+0xa4/0x140
[ 5006.964581] [<ffffffff812fa32a>] iter_file_splice_write+0x27a/0x4f0
[ 5006.964881] [<ffffffff812f8c13>] direct_splice_actor+0x53/0xd0
[ 5006.965141] [<ffffffff812f91f6>] splice_direct_to_actor+0xf6/0x390
[ 5006.965417] [<ffffffff81526c11>] ? security_file_permission+0x41/0x110
[ 5006.965708] [<ffffffff812f8bc0>] ? wakeup_pipe_writers+0x60/0x60
[ 5006.965976] [<ffffffff812f9529>] do_splice_direct+0x99/0x100
[ 5006.966228] [<ffffffff81526c11>] ? security_file_permission+0x41/0x110
[ 5006.966539] [<ffffffff812af36b>] do_sendfile+0x18b/0x6a0
[ 5006.966825] [<ffffffff812b0431>] compat_SyS_sendfile+0x71/0x80
[ 5006.967092] [<ffffffff81004875>] do_syscall_32_irqs_off+0x75/0x110
[ 5006.967382] [<ffffffff81e35903>] entry_INT80_compat+0x33/0x40
[ 5006.967653] ================================================================================
next reply other threads:[~2015-12-07 14:17 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-07 14:17 Andrey Ryabinin [this message]
2015-12-07 14:26 ` Tejun Heo
2015-12-12 23:17 ` Andy Shevchenko
2016-01-25 14:11 ` [PATCH] mm/page-writeback: fix dirty_ratelimit calculation Andrey Ryabinin
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