4.17-stable review patch. If anyone has any objections, please let me know.
------------------
From: Tejun Heo <tj@xxxxxxxxxx>
commit b512719f771a82180211c9a315b8a7f628832b3d upstream.
While forking, if delayacct init fails due to memory shortage, it
continues expecting all delayacct users to check task->delays pointer
against NULL before dereferencing it, which all of them used to do.
Commit c96f5471ce7d ("delayacct: Account blkio completion on the correct
task"), while updating delayacct_blkio_end() to take the target task
instead of always using %current, made the function test NULL on
%current->delays and then continue to operated on @p->delays. If
%current succeeded init while @p didn't, it leads to the following
crash.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
IP: __delayacct_blkio_end+0xc/0x40
PGD 8000001fd07e1067 P4D 8000001fd07e1067 PUD 1fcffbb067 PMD 0
Oops: 0000 [#1] SMP PTI
CPU: 4 PID: 25774 Comm: QIOThread0 Not tainted 4.16.0-9_fbk1_rc2_1180_g6b593215b4d7 #9
RIP: 0010:__delayacct_blkio_end+0xc/0x40
Call Trace:
try_to_wake_up+0x2c0/0x600
autoremove_wake_function+0xe/0x30
__wake_up_common+0x74/0x120
wake_up_page_bit+0x9c/0xe0
mpage_end_io+0x27/0x70
blk_update_request+0x78/0x2c0
scsi_end_request+0x2c/0x1e0
scsi_io_completion+0x20b/0x5f0
blk_mq_complete_request+0xa2/0x100
ata_scsi_qc_complete+0x79/0x400
ata_qc_complete_multiple+0x86/0xd0
ahci_handle_port_interrupt+0xc9/0x5c0
ahci_handle_port_intr+0x54/0xb0
ahci_single_level_irq_intr+0x3b/0x60
__handle_irq_event_percpu+0x43/0x190
handle_irq_event_percpu+0x20/0x50
handle_irq_event+0x2a/0x50
handle_edge_irq+0x80/0x1c0
handle_irq+0xaf/0x120
do_IRQ+0x41/0xc0
common_interrupt+0xf/0xf
Fix it by updating delayacct_blkio_end() check @p->delays instead.
Link: http://lkml.kernel.org/r/20180724175542.GP1934745@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: c96f5471ce7d ("delayacct: Account blkio completion on the correct task")
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Dave Jones <dsj@xxxxxx>
Debugged-by: Dave Jones <dsj@xxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Josh Snyder <joshs@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.15+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/delayacct.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/include/linux/delayacct.h
+++ b/include/linux/delayacct.h
@@ -124,7 +124,7 @@ static inline void delayacct_blkio_start
static inline void delayacct_blkio_end(struct task_struct *p)
{
- if (current->delays)
+ if (p->delays)
__delayacct_blkio_end(p);
delayacct_clear_flag(DELAYACCT_PF_BLKIO);
}
