On 10/10/2013 12:33 AM, Richard Weinberger wrote: > Am 09.10.2013 23:47, schrieb Jan Kara: >> On Wed 09-10-13 20:43:50, Richard Weinberger wrote: >>> CC'ing mm folks. >>> Please see below. >> Added Fenguang to CC since he is the author of this code. > > Thx, get_maintainer.pl didn't list him. > >>> Am 09.10.2013 19:26, schrieb Toralf Förster: >>>> On 10/08/2013 10:07 PM, Geert Uytterhoeven wrote: >>>>> On Sun, Oct 6, 2013 at 11:01 PM, Toralf Förster <toralf.foerster@xxxxxx> wrote: >>>>>>> Hmm, now pages_dirtied is zero, according to the backtrace, but the BUG_ON() >>>>>>> asserts its strict positive?!? >>>>>>> >>>>>>> Can you please try the following instead of the BUG_ON(): >>>>>>> >>>>>>> if (pause < 0) { >>>>>>> printk("pages_dirtied = %lu\n", pages_dirtied); >>>>>>> printk("task_ratelimit = %lu\n", task_ratelimit); >>>>>>> printk("pause = %ld\n", pause); >>>>>>> } >>>>>>> >>>>>>> Gr{oetje,eeting}s, >>>>>>> >>>>>>> Geert >>>>>> I tried it in different ways already - I'm completely unsuccessful in getting any printk output. >>>>>> As soon as the issue happens I do have a >>>>>> >>>>>> BUG: soft lockup - CPU#0 stuck for 22s! [trinity-child0:1521] >>>>>> >>>>>> at stderr of the UML and then no further input is accepted. With uml_mconsole I'm however able >>>>>> to run very basic commands like a crash dump, sysrq ond so on. >>>>> >>>>> You may get an idea of the magnitude of pages_dirtied by using a chain of >>>>> BUG_ON()s, like: >>>>> >>>>> BUG_ON(pages_dirtied > 2000000000); >>>>> BUG_ON(pages_dirtied > 1000000000); >>>>> BUG_ON(pages_dirtied > 100000000); >>>>> BUG_ON(pages_dirtied > 10000000); >>>>> BUG_ON(pages_dirtied > 1000000); >>>>> >>>>> Probably 1 million is already too much for normal operation? >>>>> >>>> period = HZ * pages_dirtied / task_ratelimit; >>>> BUG_ON(pages_dirtied > 2000000000); >>>> BUG_ON(pages_dirtied > 1000000000); <-------------- this is line 1467 >>> >>> Summary for mm people: >>> >>> Toralf runs trinty on UML/i386. >>> After some time pages_dirtied becomes very large. >>> More than 1000000000 pages in this case. >> Huh, this is really strange. pages_dirtied is passed into >> balance_dirty_pages() from current->nr_dirtied. So I wonder how a value >> over 10^9 can get there. After all that is over 4TB so I somewhat doubt the >> task was ever able to dirty that much during its lifetime (but correct me >> if I'm wrong here, with UML and memory backed disks it is not totally >> impossible)... I went through the logic of handling ->nr_dirtied but >> I didn't find any obvious problem there. Hum, maybe one thing - what >> 'task_ratelimit' values do you see in balance_dirty_pages? If that one was >> huge, we could possibly accumulate huge current->nr_dirtied. > > Toralf, you can try a snipplet like this one to get the values printed out: > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index f5236f8..a80e520 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -1463,6 +1463,12 @@ static void balance_dirty_pages(struct address_space *mapping, > goto pause; > } > period = HZ * pages_dirtied / task_ratelimit; > + > + { > + extern int printf(char *, ...); > + printf("---> task_ratelimit: %lu\n", task_ratelimit); > + } > + > pause = period; > if (current->dirty_paused_when) > pause -= now - current->dirty_paused_when; > > > Yes, printf(), not printk(). > Using this hack we print directly to host's stdout. :) > *head smack* ofc - works fine. So given this diff : iff --git a/mm/page-writeback.c b/mm/page-writeback.c index f5236f8..5a2c337 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1464,6 +1464,13 @@ static void balance_dirty_pages(struct address_space *mapping, } period = HZ * pages_dirtied / task_ratelimit; pause = period; + if (pause < 0) { + extern int printf(char *, ...); + printf("overflow : pause : %li\n", pause); + printf("overflow : pages_dirtied : %lu\n", pages_dirtied); + printf("overflow : task_ratelimit: %lu\n", task_ratelimit); + BUG_ON(1); + } if (current->dirty_paused_when) pause -= now - current->dirty_paused_when; /* @@ -1503,6 +1510,13 @@ static void balance_dirty_pages(struct address_space *mapping, } pause: + if (pause < 0) { + extern int printf(char *, ...); + printf("ick : pause : %li\n", pause); + printf("ick: pages_dirtied : %lu\n", pages_dirtied); + printf("ick: task_ratelimit: %lu\n", task_ratelimit); + BUG_ON(1); + } trace_balance_dirty_pages(bdi, dirty_thresh, background_thresh, I got this : * Starting local net.core.warnings = 0 [ ok ] ick : pause : -984 ick: pages_dirtied : 0 ick: task_ratelimit: 0 Kernel panic - not syncing: BUG! CPU: 0 PID: 1434 Comm: trinity-child2 Not tainted 3.12.0-rc4-00029-g0e7a3ed-dirty #12 47397c84 47397cb0 0841b5a0 084c30e8 085f76e0 084b4745 47397cbc 00000000 fffffc28 01fff278 085cb4a0 47397d2c 0841c5a0 084b4745 084c5398 000005ee 08432cf0 43e47600 471757f8 47397cf0 ffffff0c 47397cdc 5256d8b9 3417ec18 47397c5c: [<08060b2c>] show_stack+0x7c/0xd0 47397c7c: [<0841e34d>] dump_stack+0x26/0x28 47397c8c: [<0841b5a0>] panic+0x7a/0x180 47397cb4: [<0841c5a0>] balance_dirty_pages.isra.32+0x4e3/0x5ad 47397d30: [<080d3595>] balance_dirty_pages_ratelimited+0xf5/0x100 47397d44: [<080e4a3f>] __do_fault+0x3cf/0x440 47397d9c: [<080e6e0f>] handle_mm_fault+0xef/0x7c0 47397dec: [<080e7817>] __get_user_pages+0x227/0x420 47397e24: [<080e7ae3>] get_user_pages+0x63/0x70 47397e4c: [<08143dc6>] SyS_io_setup+0x3c6/0x760 47397eb0: [<08062984>] handle_syscall+0x64/0x80 47397ef0: [<08074fb5>] userspace+0x475/0x5f0 47397fec: [<0805f750>] fork_handler+0x60/0x70 47397ffc: [<00000000>] 0x0 EIP: 0073:[<40001282>] CPU: 0 Not tainted ESP: 007b:bfb348f8 EFLAGS: 00000246 Not tainted EAX: ffffffda EBX: 00001000 ECX: 080d0000 EDX: 80000048 ESI: 80fbff1f EDI: ffe02f77 EBP: 90f6e2a3 DS: 007b ES: 007b 47397c0c: [<0807947f>] show_regs+0x10f/0x120 47397c28: [<080623a9>] panic_exit+0x29/0x50 47397c38: [<0809ba86>] notifier_call_chain+0x36/0x60 47397c60: [<0809bba1>] __atomic_notifier_call_chain+0x21/0x30 47397c70: [<0809bbdf>] atomic_notifier_call_chain+0x2f/0x40 47397c8c: [<0841b5bc>] panic+0x96/0x180 47397cb4: [<0841c5a0>] balance_dirty_pages.isra.32+0x4e3/0x5ad 47397d30: [<080d3595>] balance_dirty_pages_ratelimited+0xf5/0x100 47397d44: [<080e4a3f>] __do_fault+0x3cf/0x440 47397d9c: [<080e6e0f>] handle_mm_fault+0xef/0x7c0 47397dec: [<080e7817>] __get_user_pages+0x227/0x420 47397e24: [<080e7ae3>] get_user_pages+0x63/0x70 47397e4c: [<08143dc6>] SyS_io_setup+0x3c6/0x760 47397eb0: [<08062984>] handle_syscall+0x64/0x80 47397ef0: [<08074fb5>] userspace+0x475/0x5f0 47397fec: [<0805f750>] fork_handler+0x60/0x70 47397ffc: [<00000000>] 0x0 /home/tfoerste/workspace/bin/start_uml.sh: line 115: 18718 Aborted (core dumped) $LINUX earlyprintk ubda=$ROOTFS ubdb=$SWAP eth0=$NET mem=$MEM $TTY umid=uml_$NAME rootfstype=ext4 "$ARGS" >From what I see there are 2 different types of issues - and this is an example of the other of both > Thanks, > //richard > -- MfG/Sincerely Toralf Förster pgp finger print: 7B1A 07F4 EC82 0F90 D4C2 8936 872A E508 7DB6 9DA3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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