Revision a9ce385344f916cd1c36a33905e564f5581beae9 authored by Jens Axboe on 15 September 2023, 19:14:23 UTC, committed by Mike Snitzer on 15 September 2023, 19:39:59 UTC
dm looks up the table for IO based on the request type, with an assumption that if the request is marked REQ_NOWAIT, it's fine to attempt to submit that IO while under RCU read lock protection. This is not OK, as REQ_NOWAIT just means that we should not be sleeping waiting on other IO, it does not mean that we can't potentially schedule. A simple test case demonstrates this quite nicely: int main(int argc, char *argv[]) { struct iovec iov; int fd; fd = open("/dev/dm-0", O_RDONLY | O_DIRECT); posix_memalign(&iov.iov_base, 4096, 4096); iov.iov_len = 4096; preadv2(fd, &iov, 1, 0, RWF_NOWAIT); return 0; } which will instantly spew: BUG: sleeping function called from invalid context at include/linux/sched/mm.h:306 in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 5580, name: dm-nowait preempt_count: 0, expected: 0 RCU nest depth: 1, expected: 0 INFO: lockdep is turned off. CPU: 7 PID: 5580 Comm: dm-nowait Not tainted 6.6.0-rc1-g39956d2dcd81 #132 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x11d/0x1b0 __might_resched+0x3c3/0x5e0 ? preempt_count_sub+0x150/0x150 mempool_alloc+0x1e2/0x390 ? mempool_resize+0x7d0/0x7d0 ? lock_sync+0x190/0x190 ? lock_release+0x4b7/0x670 ? internal_get_user_pages_fast+0x868/0x2d40 bio_alloc_bioset+0x417/0x8c0 ? bvec_alloc+0x200/0x200 ? internal_get_user_pages_fast+0xb8c/0x2d40 bio_alloc_clone+0x53/0x100 dm_submit_bio+0x27f/0x1a20 ? lock_release+0x4b7/0x670 ? blk_try_enter_queue+0x1a0/0x4d0 ? dm_dax_direct_access+0x260/0x260 ? rcu_is_watching+0x12/0xb0 ? blk_try_enter_queue+0x1cc/0x4d0 __submit_bio+0x239/0x310 ? __bio_queue_enter+0x700/0x700 ? kvm_clock_get_cycles+0x40/0x60 ? ktime_get+0x285/0x470 submit_bio_noacct_nocheck+0x4d9/0xb80 ? should_fail_request+0x80/0x80 ? preempt_count_sub+0x150/0x150 ? lock_release+0x4b7/0x670 ? __bio_add_page+0x143/0x2d0 ? iov_iter_revert+0x27/0x360 submit_bio_noacct+0x53e/0x1b30 submit_bio_wait+0x10a/0x230 ? submit_bio_wait_endio+0x40/0x40 __blkdev_direct_IO_simple+0x4f8/0x780 ? blkdev_bio_end_io+0x4c0/0x4c0 ? stack_trace_save+0x90/0xc0 ? __bio_clone+0x3c0/0x3c0 ? lock_release+0x4b7/0x670 ? lock_sync+0x190/0x190 ? atime_needs_update+0x3bf/0x7e0 ? timestamp_truncate+0x21b/0x2d0 ? inode_owner_or_capable+0x240/0x240 blkdev_direct_IO.part.0+0x84a/0x1810 ? rcu_is_watching+0x12/0xb0 ? lock_release+0x4b7/0x670 ? blkdev_read_iter+0x40d/0x530 ? reacquire_held_locks+0x4e0/0x4e0 ? __blkdev_direct_IO_simple+0x780/0x780 ? rcu_is_watching+0x12/0xb0 ? __mark_inode_dirty+0x297/0xd50 ? preempt_count_add+0x72/0x140 blkdev_read_iter+0x2a4/0x530 do_iter_readv_writev+0x2f2/0x3c0 ? generic_copy_file_range+0x1d0/0x1d0 ? fsnotify_perm.part.0+0x25d/0x630 ? security_file_permission+0xd8/0x100 do_iter_read+0x31b/0x880 ? import_iovec+0x10b/0x140 vfs_readv+0x12d/0x1a0 ? vfs_iter_read+0xb0/0xb0 ? rcu_is_watching+0x12/0xb0 ? rcu_is_watching+0x12/0xb0 ? lock_release+0x4b7/0x670 do_preadv+0x1b3/0x260 ? do_readv+0x370/0x370 __x64_sys_preadv2+0xef/0x150 do_syscall_64+0x39/0xb0 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f5af41ad806 Code: 41 54 41 89 fc 55 44 89 c5 53 48 89 cb 48 83 ec 18 80 3d e4 dd 0d 00 00 74 7a 45 89 c1 49 89 ca 45 31 c0 b8 47 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 be 00 00 00 48 85 c0 79 4a 48 8b 0d da 55 RSP: 002b:00007ffd3145c7f0 EFLAGS: 00000246 ORIG_RAX: 0000000000000147 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5af41ad806 RDX: 0000000000000001 RSI: 00007ffd3145c850 RDI: 0000000000000003 RBP: 0000000000000008 R08: 0000000000000000 R09: 0000000000000008 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003 R13: 00007ffd3145c850 R14: 000055f5f0431dd8 R15: 0000000000000001 </TASK> where in fact it is dm itself that attempts to allocate a bio clone with GFP_NOIO under the rcu read lock, regardless of the request type. Fix this by getting rid of the special casing for REQ_NOWAIT, and just use the normal SRCU protected table lookup. Get rid of the bio based table locking helpers at the same time, as they are now unused. Cc: stable@vger.kernel.org Fixes: 563a225c9fd2 ("dm: introduce dm_{get,put}_live_table_bio called from dm_submit_bio") Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
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overlay-notes.rst
.. SPDX-License-Identifier: GPL-2.0
========================
Devicetree Overlay Notes
========================
This document describes the implementation of the in-kernel
device tree overlay functionality residing in drivers/of/overlay.c and is a
companion document to Documentation/devicetree/dynamic-resolution-notes.rst[1]
How overlays work
-----------------
A Devicetree's overlay purpose is to modify the kernel's live tree, and
have the modification affecting the state of the kernel in a way that
is reflecting the changes.
Since the kernel mainly deals with devices, any new device node that result
in an active device should have it created while if the device node is either
disabled or removed all together, the affected device should be deregistered.
Lets take an example where we have a foo board with the following base tree::
---- foo.dts ---------------------------------------------------------------
/* FOO platform */
/dts-v1/;
/ {
compatible = "corp,foo";
/* shared resources */
res: res {
};
/* On chip peripherals */
ocp: ocp {
/* peripherals that are always instantiated */
peripheral1 { ... };
};
};
---- foo.dts ---------------------------------------------------------------
The overlay bar.dts,
::
---- bar.dts - overlay target location by label ----------------------------
/dts-v1/;
/plugin/;
&ocp {
/* bar peripheral */
bar {
compatible = "corp,bar";
... /* various properties and child nodes */
};
};
---- bar.dts ---------------------------------------------------------------
when loaded (and resolved as described in [1]) should result in foo+bar.dts::
---- foo+bar.dts -----------------------------------------------------------
/* FOO platform + bar peripheral */
/ {
compatible = "corp,foo";
/* shared resources */
res: res {
};
/* On chip peripherals */
ocp: ocp {
/* peripherals that are always instantiated */
peripheral1 { ... };
/* bar peripheral */
bar {
compatible = "corp,bar";
... /* various properties and child nodes */
};
};
};
---- foo+bar.dts -----------------------------------------------------------
As a result of the overlay, a new device node (bar) has been created
so a bar platform device will be registered and if a matching device driver
is loaded the device will be created as expected.
If the base DT was not compiled with the -@ option then the "&ocp" label
will not be available to resolve the overlay node(s) to the proper location
in the base DT. In this case, the target path can be provided. The target
location by label syntax is preferred because the overlay can be applied to
any base DT containing the label, no matter where the label occurs in the DT.
The above bar.dts example modified to use target path syntax is::
---- bar.dts - overlay target location by explicit path --------------------
/dts-v1/;
/plugin/;
&{/ocp} {
/* bar peripheral */
bar {
compatible = "corp,bar";
... /* various properties and child nodes */
}
};
---- bar.dts ---------------------------------------------------------------
Overlay in-kernel API
--------------------------------
The API is quite easy to use.
1) Call of_overlay_fdt_apply() to create and apply an overlay changeset. The
return value is an error or a cookie identifying this overlay.
2) Call of_overlay_remove() to remove and cleanup the overlay changeset
previously created via the call to of_overlay_fdt_apply(). Removal of an
overlay changeset that is stacked by another will not be permitted.
Finally, if you need to remove all overlays in one-go, just call
of_overlay_remove_all() which will remove every single one in the correct
order.
There is the option to register notifiers that get called on
overlay operations. See of_overlay_notifier_register/unregister and
enum of_overlay_notify_action for details.
A notifier callback for OF_OVERLAY_PRE_APPLY, OF_OVERLAY_POST_APPLY, or
OF_OVERLAY_PRE_REMOVE may store pointers to a device tree node in the overlay
or its content but these pointers must not persist past the notifier callback
for OF_OVERLAY_POST_REMOVE. The memory containing the overlay will be
kfree()ed after OF_OVERLAY_POST_REMOVE notifiers are called. Note that the
memory will be kfree()ed even if the notifier for OF_OVERLAY_POST_REMOVE
returns an error.
The changeset notifiers in drivers/of/dynamic.c are a second type of notifier
that could be triggered by applying or removing an overlay. These notifiers
are not allowed to store pointers to a device tree node in the overlay
or its content. The overlay code does not protect against such pointers
remaining active when the memory containing the overlay is freed as a result
of removing the overlay.
Any other code that retains a pointer to the overlay nodes or data is
considered to be a bug because after removing the overlay the pointer
will refer to freed memory.
Users of overlays must be especially aware of the overall operations that
occur on the system to ensure that other kernel code does not retain any
pointers to the overlay nodes or data. Any example of an inadvertent use
of such pointers is if a driver or subsystem module is loaded after an
overlay has been applied, and the driver or subsystem scans the entire
devicetree or a large portion of it, including the overlay nodes.
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