The patch titled Subject: mm: swapfile: fix cluster reclaim work crash on rotational devices has been added to the -mm mm-unstable branch. Its filename is mm-swapfile-fix-cluster-reclaim-work-crash-on-rotational-devices.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swapfile-fix-cluster-reclaim-work-crash-on-rotational-devices.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Johannes Weiner <hannes@xxxxxxxxxxx> Subject: mm: swapfile: fix cluster reclaim work crash on rotational devices Date: Thu, 7 Nov 2024 09:08:36 -0500 syzbot and Daan report a NULL pointer crash in the new full swap cluster reclaim work: > Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN PTI > KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] > CPU: 1 UID: 0 PID: 51 Comm: kworker/1:1 Not tainted 6.12.0-rc6-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 > Workqueue: events swap_reclaim_work > RIP: 0010:__list_del_entry_valid_or_report+0x20/0x1c0 lib/list_debug.c:49 > Code: 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 89 fe 48 83 c7 08 48 83 ec 18 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 19 01 00 00 48 89 f2 48 8b 4e 08 48 b8 00 00 00 > RSP: 0018:ffffc90000bb7c30 EFLAGS: 00010202 > RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff88807b9ae078 > RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000008 > RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000 > R10: 0000000000000001 R11: 000000000000004f R12: dffffc0000000000 > R13: ffffffffffffffb8 R14: ffff88807b9ae000 R15: ffffc90003af1000 > FS: 0000000000000000(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fffaca68fb8 CR3: 00000000791c8000 CR4: 00000000003526f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > <TASK> > __list_del_entry_valid include/linux/list.h:124 [inline] > __list_del_entry include/linux/list.h:215 [inline] > list_move_tail include/linux/list.h:310 [inline] > swap_reclaim_full_clusters+0x109/0x460 mm/swapfile.c:748 > swap_reclaim_work+0x2e/0x40 mm/swapfile.c:779 The syzbot console output indicates a virtual environment where swapfile is on a rotational device. In this case, clusters aren't actually used, and si->full_clusters is not initialized. Daan's report is from qemu, so likely rotational too. Make sure to only schedule the cluster reclaim work when clusters are actually in use. Link: https://lkml.kernel.org/r/20241107142335.GB1172372@xxxxxxxxxxx Link: https://lore.kernel.org/lkml/672ac50b.050a0220.2edce.1517.GAE@xxxxxxxxxx/ Link: https://github.com/systemd/systemd/issues/35044 Fixes: 5168a68eb78f ("mm, swap: avoid over reclaim of full clusters") Reported-by: syzbot+078be8bfa863cb9e0c6b@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Reported-by: Daan De Meyer <daan.j.demeyer@xxxxxxxxx> Cc: Kairui Song <ryncsn@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/swapfile.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/swapfile.c~mm-swapfile-fix-cluster-reclaim-work-crash-on-rotational-devices +++ a/mm/swapfile.c @@ -929,7 +929,7 @@ static void swap_range_alloc(struct swap si->highest_bit = 0; del_from_avail_list(si); - if (vm_swap_full()) + if (si->cluster_info && vm_swap_full()) schedule_work(&si->reclaim_work); } } _ Patches currently in -mm which might be from hannes@xxxxxxxxxxx are mm-swapfile-fix-cluster-reclaim-work-crash-on-rotational-devices.patch