On Fri, Feb 12, 2021 at 4:43 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Fri 12-02-21 21:58:15, Tetsuo Handa wrote: > > On 2021/02/12 21:30, Michal Hocko wrote: > > > On Fri 12-02-21 12:22:07, Matthew Wilcox wrote: > > >> On Fri, Feb 12, 2021 at 08:18:11PM +0900, Tetsuo Handa wrote: > > >>> On 2021/02/12 1:41, Michal Hocko wrote: > > >>>> But I suspect we have drifted away from the original issue. I thought > > >>>> that a simple check would help us narrow down this particular case and > > >>>> somebody messing up from the IRQ context didn't sound like a completely > > >>>> off. > > >>>> > > >>> > > >>> From my experience at https://lkml.kernel.org/r/201409192053.IHJ35462.JLOMOSOFFVtQFH@xxxxxxxxxxxxxxxxxxx , > > >>> I think we can replace direct PF_* manipulation with macros which do not receive "struct task_struct *" argument. > > >>> Since TASK_PFA_TEST()/TASK_PFA_SET()/TASK_PFA_CLEAR() are for manipulating PFA_* flags on a remote thread, we can > > >>> define similar ones for manipulating PF_* flags on current thread. Then, auditing dangerous users becomes easier. > > >> > > >> No, nobody is manipulating another task's GFP flags. > > > > > > Agreed. And nobody should be manipulating PF flags on remote tasks > > > either. > > > > > > > No. You are misunderstanding. The bug report above is an example of > > manipulating PF flags on remote tasks. > > The bug report you are referring to is ancient. And the cpuset code > doesn't touch task->flags for a long time. I haven't checked exactly but > it is years since regular and atomic flags have been separated unless I > misremember. > > > You say "nobody should", but the reality is "there indeed was". There > > might be unnoticed others. The point of this proposal is to make it > > possible to "find such unnoticed users who are manipulating PF flags > > on remote tasks". > > I am really confused what you are proposing here TBH and referring to an > ancient bug doesn't really help. task->flags are _explicitly_ documented > to be only used for _current_. Is it possible that somebody writes a > buggy code? Sure, should we build a whole infrastructure around that to > catch such a broken code? I am not really sure. One bug 6 years ago > doesn't sound like a good reason for that. Another similar one was just reported: https://syzkaller.appspot.com/bug?extid=1b2c6989ec12e467d65c WARNING: possible circular locking dependency detected 5.11.0-rc7-syzkaller #0 Not tainted ------------------------------------------------------ kswapd0/2232 is trying to acquire lock: ffff88801f552650 (sb_internal){.+.+}-{0:0}, at: evict+0x2ed/0x6b0 fs/inode.c:577 but task is already holding lock: ffffffff8be89240 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 mm/page_alloc.c:5195 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (fs_reclaim){+.+.}-{0:0}: __fs_reclaim_acquire mm/page_alloc.c:4326 [inline] fs_reclaim_acquire+0x117/0x150 mm/page_alloc.c:4340 might_alloc include/linux/sched/mm.h:193 [inline] slab_pre_alloc_hook mm/slab.h:493 [inline] slab_alloc_node mm/slab.c:3221 [inline] kmem_cache_alloc_node_trace+0x48/0x520 mm/slab.c:3596 __do_kmalloc_node mm/slab.c:3618 [inline] __kmalloc_node+0x38/0x60 mm/slab.c:3626 kmalloc_node include/linux/slab.h:575 [inline] kvmalloc_node+0x61/0xf0 mm/util.c:587 kvmalloc include/linux/mm.h:781 [inline] ext4_xattr_inode_cache_find fs/ext4/xattr.c:1465 [inline] ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1508 [inline] ext4_xattr_set_entry+0x1ce6/0x3780 fs/ext4/xattr.c:1649 ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2224 ext4_xattr_set_handle+0x8f4/0x13e0 fs/ext4/xattr.c:2380 ext4_xattr_set+0x13a/0x340 fs/ext4/xattr.c:2493 __vfs_setxattr+0x10e/0x170 fs/xattr.c:177 __vfs_setxattr_noperm+0x11a/0x4c0 fs/xattr.c:208 __vfs_setxattr_locked+0x1bf/0x250 fs/xattr.c:266 vfs_setxattr+0x135/0x320 fs/xattr.c:291 setxattr+0x1ff/0x290 fs/xattr.c:553 path_setxattr+0x170/0x190 fs/xattr.c:572 __do_sys_setxattr fs/xattr.c:587 [inline] __se_sys_setxattr fs/xattr.c:583 [inline] __x64_sys_setxattr+0xc0/0x160 fs/xattr.c:583 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
