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Date: Tue, 18 Nov 2014 22:44:02 -0500 From: Sasha Levin <sasha.levin@...cle.com> To: Andrew Morton <akpm@...ux-foundation.org> CC: Hugh Dickins <hughd@...gle.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Dave Jones <davej@...hat.com>, Jens Axboe <axboe@...nel.dk> Subject: Re: mm: shmem: freeing mlocked page On 11/18/2014 04:58 PM, Andrew Morton wrote: > On Fri, 14 Nov 2014 09:39:40 -0500 Sasha Levin <sasha.levin@...cle.com> wrote: > >> >> [ 1026.988043] BUG: Bad page state in process trinity-c374 pfn:23f70 >> [ 1026.989684] page:ffffea0000b3d300 count:0 mapcount:0 mapping: (null) index:0x5b >> [ 1026.991151] flags: 0x1fffff8028000c(referenced|uptodate|swapbacked|mlocked) >> [ 1026.992410] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set >> [ 1026.993479] bad because of flags: >> [ 1026.994125] flags: 0x200000(mlocked) > > Gee that new page dumping code is nice! > >> [ 1026.994816] Modules linked in: >> [ 1026.995378] CPU: 7 PID: 7879 Comm: trinity-c374 Not tainted 3.18.0-rc4-next-20141113-sasha-00047-gd1763ce-dirty #1455 >> [ 1026.996123] FAULT_INJECTION: forcing a failure. >> [ 1026.996123] name failslab, interval 100, probability 30, space 0, times -1 >> [ 1026.999050] 0000000000000000 0000000000000000 0000000000b3d300 ffff88061295bbd8 >> [ 1027.000676] ffffffff92f71097 0000000000000000 ffffea0000b3d300 ffff88061295bc08 >> [ 1027.002020] ffffffff8197ef7a ffffea0000b3d300 ffffffff942dd148 dfffe90000000000 >> [ 1027.003359] Call Trace: >> [ 1027.003831] dump_stack (lib/dump_stack.c:52) >> [ 1027.004725] bad_page (mm/page_alloc.c:338) >> [ 1027.005623] free_pages_prepare (mm/page_alloc.c:657 mm/page_alloc.c:763) >> [ 1027.006761] free_hot_cold_page (mm/page_alloc.c:1438) >> [ 1027.007772] ? __page_cache_release (mm/swap.c:66) >> [ 1027.008815] put_page (mm/swap.c:270) >> [ 1027.009665] page_cache_pipe_buf_release (fs/splice.c:93) >> [ 1027.010888] __splice_from_pipe (fs/splice.c:784 fs/splice.c:886) >> [ 1027.011917] ? might_fault (./arch/x86/include/asm/current.h:14 mm/memory.c:3734) >> [ 1027.012856] ? pipe_lock (fs/pipe.c:69) >> [ 1027.013728] ? write_pipe_buf (fs/splice.c:1534) >> [ 1027.014756] vmsplice_to_user (fs/splice.c:1574) >> [ 1027.015725] ? rcu_read_lock_held (kernel/rcu/update.c:169) >> [ 1027.016757] ? __fget_light (include/linux/fdtable.h:80 fs/file.c:684) >> [ 1027.017782] SyS_vmsplice (fs/splice.c:1656 fs/splice.c:1639) >> [ 1027.018863] tracesys_phase2 (arch/x86/kernel/entry_64.S:529) >> > > So what happened here? Userspace fed some mlocked memory into splice() > and then, while splice() was running, userspace dropped its reference > to the memory, leaving splice() with the last reference. Yet somehow, > that page was still marked as being mlocked. I wouldn't expect the > kernel to permit userspace to drop its reference to the memory without > first clearing the mlocked state. > > Is it possible to work out from trinity sources what the exact sequence > was? Which syscalls are being used, for example? Trinity can't really log anything because attempts to log syscalls slow everything down to a crawl to the point nothing reproduces. I've just looked at that trace above, and got a bit more confused. I didn't think that you can mlock page cache. How would a user do that exactly? Thanks, Sasha -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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