On Thu 24-07-14 08:34:56, Johannes Weiner wrote: [...] > Would it be better to move mem_cgroup_oom_notify() directly into the > trylock function while the memcg_oom_lock is still held? I don't know. It sounds like mixing two things together. I would rather keep them separate unless we have a good reason to do otherwise. Sharing the same lock is just a coincidence mostly required for the registration code to not miss event. > > Let's go with simpler route for now as this is not a hot path, though. > > --- > > >From 2c2642dbfb3f7d8c9f20f7793850426daa770078 Mon Sep 17 00:00:00 2001 > > From: Michal Hocko <mhocko@xxxxxxx> > > Date: Thu, 24 Jul 2014 14:00:39 +0200 > > Subject: [PATCH] memcg: oom_notify use-after-free fix > > > > Paul Furtado has reported the following GPF: > > general protection fault: 0000 [#1] SMP > > Modules linked in: ipv6 dm_mod xen_netfront coretemp hwmon x86_pkg_temp_thermal crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel ablk_helper cryptd lrw gf128mul glue_helper aes_x86_64 microcode pcspkr ext4 jbd2 mbcache raid0 xen_blkfront > > CPU: 3 PID: 3062 Comm: java Not tainted 3.16.0-rc5 #1 > > task: ffff8801cfe8f170 ti: ffff8801d2ec4000 task.ti: ffff8801d2ec4000 > > RIP: e030:[<ffffffff811c0b80>] [<ffffffff811c0b80>] mem_cgroup_oom_synchronize+0x140/0x240 > > RSP: e02b:ffff8801d2ec7d48 EFLAGS: 00010283 > > RAX: 0000000000000001 RBX: ffff88009d633800 RCX: 000000000000000e > > RDX: fffffffffffffffe RSI: ffff88009d630200 RDI: ffff88009d630200 > > RBP: ffff8801d2ec7da8 R08: 0000000000000012 R09: 00000000fffffffe > > R10: 0000000000000000 R11: 0000000000000000 R12: ffff88009d633800 > > R13: ffff8801d2ec7d48 R14: dead000000100100 R15: ffff88009d633a30 > > FS: 00007f1748bb4700(0000) GS:ffff8801def80000(0000) knlGS:0000000000000000 > > CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b > > CR2: 00007f4110300308 CR3: 00000000c05f7000 CR4: 0000000000002660 > > Stack: > > ffff88009d633800 0000000000000000 ffff8801cfe8f170 ffffffff811bae10 > > ffffffff81ca73f8 ffffffff81ca73f8 ffff8801d2ec7dc8 0000000000000006 > > 00000000e3b30000 00000000e3b30000 ffff8801d2ec7f58 0000000000000001 > > Call Trace: > > [<ffffffff811bae10>] ? mem_cgroup_wait_acct_move+0x110/0x110 > > [<ffffffff81159628>] pagefault_out_of_memory+0x18/0x90 > > [<ffffffff8105cee9>] mm_fault_error+0xa9/0x1a0 > > [<ffffffff8105d488>] __do_page_fault+0x478/0x4c0 > > [<ffffffff81004f00>] ? xen_mc_flush+0xb0/0x1b0 > > [<ffffffff81003ab3>] ? xen_write_msr_safe+0xa3/0xd0 > > [<ffffffff81012a40>] ? __switch_to+0x2d0/0x600 > > [<ffffffff8109e273>] ? finish_task_switch+0x53/0xf0 > > [<ffffffff81643b0a>] ? __schedule+0x37a/0x6d0 > > [<ffffffff8105d5dc>] do_page_fault+0x2c/0x40 > > [<ffffffff81649858>] page_fault+0x28/0x30 > > Code: 44 00 00 48 89 df e8 40 ca ff ff 48 85 c0 49 89 c4 74 35 4c 8b b0 30 02 00 00 4c 8d b8 30 02 00 00 4d 39 fe 74 1b 0f 1f 44 00 00 <49> 8b 7e 10 be 01 00 00 00 e8 42 d2 04 00 4d 8b 36 4d 39 fe 75 > > RIP [<ffffffff811c0b80>] mem_cgroup_oom_synchronize+0x140/0x240 > > RSP <ffff8801d2ec7d48> > > ---[ end trace 050b00c5503ce96a ]--- > > > > fb2a6fc56be6 (mm: memcg: rework and document OOM waiting and wakeup) has > > moved mem_cgroup_oom_notify outside of memcg_oom_lock assuming it is > > protected by the hierarchical OOM-lock. Although this is true for the > > notification part the protection doesn't cover unregistration of event > > which can happen in parallel now so mem_cgroup_oom_notify can see > > already unlinked and/or freed mem_cgroup_eventfd_list. > > > > Fix this by using memcg_oom_lock also in mem_cgroup_oom_notify. > > > > Reported-by: Paul Furtado <paulfurtado91@xxxxxxxxx> > > Fixes: fb2a6fc56be6 (mm: memcg: rework and document OOM waiting and wakeup) > > Cc: stable@xxxxxxxxxxxxxxx # 3.12+ > > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> > > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Thanks! -- Michal Hocko SUSE Labs -- 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>