Before commit 452b94b8c8 ("mm/swap: don't BUG_ON() due to
uninitialized swap slot cache"), the following bug is reported,
------------[ cut here ]------------
kernel BUG at mm/swap_slots.c:270!
invalid opcode: 0000 [#1] SMP
CPU: 5 PID: 1745 Comm: (sd-pam) Not tainted 4.11.0-rc1-00243-g24c534bb161b #1
Hardware name: System manufacturer System Product Name/Z170-K, BIOS 1803 05/06/2016
RIP: 0010:free_swap_slot+0xba/0xd0
Call Trace:
swap_free+0x36/0x40
do_swap_page+0x360/0x6d0
__handle_mm_fault+0x880/0x1080
handle_mm_fault+0xd0/0x240
__do_page_fault+0x232/0x4d0
do_page_fault+0x20/0x70
page_fault+0x22/0x30
---[ end trace aefc9ede53e0ab21 ]---
This is raised by the BUG_ON(!swap_slot_cache_initialized) in
free_swap_slot(). This is incorrect, because even if the swap slots
cache fails to be initialized, the swap should operate properly without
the swap slots cache. And the use_swap_slot_cache check later in the
function will protect the uninitialized swap slots cache case.
In commit 452b94b8c8, the BUG_ON() is replaced by WARN_ON_ONCE(). In
the patch, the WARN_ON_ONCE() is removed too.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This BUG_ON() triggered for me once at shutdown, and I don't see a
reason for the check. The code correctly checks whether the swap slot
cache is usable or not, so an uninitialized swap slot cache is not
actually problematic afaik.
I've temporarily just switched the BUG_ON() to a WARN_ON_ONCE(), since
I'm not sure why that seemingly pointless check was there. I suspect
the real fix is to just remove it entirely, but for now we'll warn about
it but not bring the machine down.
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Because during swap off, a swap entry may have swap_map[] ==
SWAP_HAS_CACHE (for example, just allocated). If we return NULL in
__read_swap_cache_async(), the swap off will abort. So when swap slot
cache is disabled, (for swap off), we will wait for page to be put into
swap cache in such race condition. This should not be a problem for swap
slot cache, because swap slot cache should be drained after clearing
swap_slot_cache_enabled.
[ying.huang@intel.com: fix memory leak in __read_swap_cache_async()]
Link: http://lkml.kernel.org/r/874lzt6znd.fsf@yhuang-dev.intel.com
Link: http://lkml.kernel.org/r/5e2c5f6abe8e6eb0797408897b1bba80938e9b9d.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net> escreveu:
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We add per cpu caches for swap slots that can be allocated and freed
quickly without the need to touch the swap info lock.
Two separate caches are maintained for swap slots allocated and swap
slots returned. This is to allow the swap slots to be returned to the
global pool in a batch so they will have a chance to be coaelesced with
other slots in a cluster. We do not reuse the slots that are returned
right away, as it may increase fragmentation of the slots.
The swap allocation cache is protected by a mutex as we may sleep when
searching for empty slots in cache. The swap free cache is protected by
a spin lock as we cannot sleep in the free path.
We refill the swap slots cache when we run out of slots, and we disable
the swap slots cache and drain the slots if the global number of slots
fall below a low watermark threshold. We re-enable the cache agian when
the slots available are above a high watermark.
[ying.huang@intel.com: use raw_cpu_ptr over this_cpu_ptr for swap slots access]
[tim.c.chen@linux.intel.com: add comments on locks in swap_slots.h]
Link: http://lkml.kernel.org/r/20170118180327.GA24225@linux.intel.com
Link: http://lkml.kernel.org/r/35de301a4eaa8daa2977de6e987f2c154385eb66.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Michal Hocko <mhocko@suse.com>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net> escreveu:
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Huang Ying