Re: scsi: non atomic allocation in mempool_alloc in atomic context

[Douglas Gilbert]

On 14-12-31 01:14 PM, Sasha Levin wrote:
> Hi Christoph,
>
> I'm seeing an issue which was bisected down to 3c356bde1 ("scsi: stop passing
> a gfp_mask argument down the command setup path"):
>
> [ 3395.328221] BUG: sleeping function called from invalid context at mm/mempool.c:206
> [ 3395.329540] in_atomic(): 1, irqs_disabled(): 0, pid: 6399, name: trinity-c531
> [ 3395.331104] no locks held by trinity-c531/6399.
> [ 3395.331849] Preemption disabled blk_execute_rq_nowait (block/blk-exec.c:95)
> [ 3395.333145]
> [ 3395.333392] CPU: 5 PID: 6399 Comm: trinity-c531 Not tainted 3.19.0-rc1-next-20141226-sasha-00051-g2dd3d73 #1646
> [ 3395.335266]  0000000000000000 0000000000000000 ffff880608948000 ffff880645a07548
> [ 3395.337679]  ffffffff9137c79d 0000000000000000 ffff880608948000 ffff880645a07588
> [ 3395.340220]  ffffffff814ad713 ffffffff9de20590 ffff880608948000 ffffffff926a166c
> [ 3395.342643] Call Trace:
> [ 3395.345099] dump_stack (lib/dump_stack.c:52)
> [ 3395.346793] ___might_sleep (kernel/sched/core.c:7342)
> [ 3395.348571] __might_sleep (kernel/sched/core.c:7308)
> [ 3395.351944] mempool_alloc (mm/mempool.c:206 (discriminator 1))
> [ 3395.355196] scsi_sg_alloc (drivers/scsi/scsi_lib.c:582)
> [ 3395.356893] __sg_alloc_table (lib/scatterlist.c:282)
> [ 3395.358844] ? sdev_disable_disk_events (drivers/scsi/scsi_lib.c:577)
> [ 3395.360873] scsi_alloc_sgtable (drivers/scsi/scsi_lib.c:608)
> [ 3395.362769] scsi_init_sgtable (drivers/scsi/scsi_lib.c:1087)
> [ 3395.364583] ? lockdep_init_map (kernel/locking/lockdep.c:2986)
> [ 3395.366354] scsi_init_io (drivers/scsi/scsi_lib.c:1122)
> [ 3395.368092] ? do_init_timer (kernel/time/timer.c:669)
> [ 3395.369837] scsi_setup_cmnd (drivers/scsi/scsi_lib.c:1220 drivers/scsi/scsi_lib.c:1268)
> [ 3395.371743] scsi_queue_rq (drivers/scsi/scsi_lib.c:1875 drivers/scsi/scsi_lib.c:1980)
> [ 3395.373471] __blk_mq_run_hw_queue (block/blk-mq.c:751)
> [ 3395.375481] blk_mq_run_hw_queue (block/blk-mq.c:831)
> [ 3395.377324] blk_mq_insert_request (block/blk-mq.h:92 block/blk-mq.c:974)
> [ 3395.379377] ? blk_rq_map_user (block/blk-map.c:78 block/blk-map.c:142)
> [ 3395.381307] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2559 kernel/locking/lockdep.c:2601)
> [ 3395.383485] blk_execute_rq_nowait (block/blk-exec.c:95)
> [ 3395.386995] sg_common_write.isra.2 (drivers/scsi/sg.c:823)
> [ 3395.388712] ? might_fault (mm/memory.c:3730)
> [ 3395.390624] sg_write (drivers/scsi/sg.c:686)
> [ 3395.403014] do_loop_readv_writev (fs/read_write.c:722)
> [ 3395.407429] do_readv_writev (fs/read_write.c:854)
> [ 3395.415486] vfs_writev (fs/read_write.c:893)
> [ 3395.417116] SyS_writev (fs/read_write.c:926 fs/read_write.c:917)
> [ 3395.418851] ? trace_hardirqs_on_thunk (arch/x86/lib/thunk_64.S:33)
> [ 3395.420922] system_call_fastpath (arch/x86/kernel/entry_64.S:423)

Looks interesting: vfs injecting SCSI commands with iovec
through the sg driver's async interface.


The problem seems to be here in scsi_lib.c, mq=true:

static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents, bool mq)
{
        struct scatterlist *first_chunk = NULL;
        gfp_t gfp_mask = mq ? GFP_NOIO : GFP_ATOMIC;
        int ret;
...

What is the downside of setting gfp_mask to GFP_ATOMIC
in all cases?

Doug Gilbert


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