Merge branch 'fixes for concurrent htab updates'

Hou Tao says:

====================

From: Hou Tao <houtao1@huawei.com>

Hi,

The patchset aims to fix the issues found during investigating the
syzkaller problem reported in [0]. It seems that the concurrent updates
to the same hash-table bucket may fail as shown in patch 1.

Patch 1 uses preempt_disable() to fix the problem for
htab_use_raw_lock() case. For !htab_use_raw_lock() case, the problem is
left to "BPF specific memory allocator" patchset [1] in which
!htab_use_raw_lock() will be removed.

Patch 2 fixes the out-of-bound memory read problem reported in [0]. The
problem has the root cause as patch 1 and it is fixed by handling -EBUSY
from htab_lock_bucket() correctly.

Patch 3 add two cases for hash-table update: one for the reentrancy of
bpf_map_update_elem(), and another one for concurrent updates of the
same hash-table bucket.

Comments are always welcome.

Regards,
Tao

[0]: https://lore.kernel.org/bpf/CACkBjsbuxaR6cv0kXJoVnBfL9ZJXjjoUcMpw_Ogc313jSrg14A@mail.gmail.com/
[1]: https://lore.kernel.org/bpf/20220819214232.18784-1-alexei.starovoitov@gmail.com/

Change Log:

v4:
 * rebased on bpf-next
 * add htab_update to DENYLIST.s390x

v3: https://lore.kernel.org/bpf/20220829023709.1958204-1-houtao@huaweicloud.com/
 * patch 1: update commit message and add Fixes tag
 * patch 2: add Fixes tag
 * patch 3: elaborate the description of test cases

v2: https://lore.kernel.org/bpf/bd60ef93-1c6a-2db2-557d-b09b92ad22bd@huaweicloud.com/
 * Note the fix is for CONFIG_PREEMPT case in commit message and add
   Reviewed-by tag for patch 1
 * Drop patch "bpf: Allow normally concurrent map updates for !htab_use_raw_lock() case"

v1: https://lore.kernel.org/bpf/20220821033223.2598791-1-houtao@huaweicloud.com/
====================

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>