On 02/09/2015 08:14 AM, Konstantin Khlebnikov wrote: > Python was running under ptrace-based sandbox "sydbox" used exherbo > chroot. Kernel: 3.18.6 + my patch "mm: prevent endless growth of > anon_vma hierarchy" (patch seems stable). > > [ 4674.087780] INFO: task python:25873 blocked for more than 120 seconds. > [ 4674.087793] Tainted: G U 3.18.6-zurg+ #158 > [ 4674.087797] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > [ 4674.087801] python D ffff88041e2d2000 14176 25873 25630 0x00000102 > [ 4674.087817] ffff880286247b68 0000000000000086 ffff8803d5fe6b40 > 0000000000012000 > [ 4674.087824] ffff880286247fd8 0000000000012000 ffff88040c16eb40 > ffff8803d5fe6b40 > [ 4674.087830] 0000000300000003 ffff8803d5fe6b40 ffff880362888e78 > ffff880362888e60 > [ 4674.087836] Call Trace: > [ 4674.087854] [<ffffffff81696be9>] schedule+0x29/0x70 > [ 4674.087865] [<ffffffff81699815>] rwsem_down_write_failed+0x1d5/0x2f0 > [ 4674.087873] [<ffffffff812d4c73>] call_rwsem_down_write_failed+0x13/0x20 > [ 4674.087881] [<ffffffff816990c1>] ? down_write+0x31/0x50 > [ 4674.087891] [<ffffffff811f3b44>] do_coredump+0x144/0xee0 > [ 4674.087900] [<ffffffff810b66f7>] ? pick_next_task_fair+0x397/0x450 > [ 4674.087909] [<ffffffff810026a6>] ? __switch_to+0x1d6/0x5f0 > [ 4674.087915] [<ffffffff816966e6>] ? __schedule+0x3a6/0x880 > [ 4674.087924] [<ffffffff81690000>] ? klist_remove+0x40/0xd0 > [ 4674.087932] [<ffffffff81093988>] get_signal+0x298/0x6b0 > [ 4674.087940] [<ffffffff81003588>] do_signal+0x28/0xbb0 > [ 4674.087946] [<ffffffff8109276d>] ? do_send_sig_info+0x5d/0x80 > [ 4674.087955] [<ffffffff81004179>] do_notify_resume+0x69/0xb0 > [ 4674.087963] [<ffffffff8169b028>] int_signal+0x12/0x17 > > Maybe this guy did something wrong? Well he has do_coredump on stack, so he did something wrong in userspace? But here he's just waiting on down_write. Unless there's some bug in do_coredump that would lock for read and then for write, without an unlock in between? > Looks like mmap_sem is locked for read: So we have the python waiting for write, blocking all new readers (that's how read/write locks work, right?), but itself waiting for a prior reader to finish. The question is, who is/was the reader? You could search the mmap_sem or mm address in the rest of the processes' stacks, and maybe you'll find him? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>