uio_hv_generic: Fix ring buffer sysfs creation path
v7 cover uio_hv_generic: Fix ring buffer sysfs creation path
Hi,
This patch series aims to address the sysfs creation issue for the ring buffer by reorganizing the code. Additionally, it updates the ring sysfs size to accurately reflect the actual ring buffer size, rather than a fixed static value.
PFB change logs:
Changes since v6:
https://lore.kernel.org/all/[email protected]/
* Rebased to 6.15-rc4 tip where [1] is not present to fix compilation issue on 6.15-rc4 and to enable porting of the fix to previous kernel versions where patch [1] is not present. (addressed Greg's comments)
* Note: continued to use bin_attrs and not bin_attrs_new so that the fix can be ported to older kernels where bin_attrs_new was not introduced.
[1]: commit 9bec944506fa ("sysfs: constify attribute_group::bin_attrs")
Changes since v5:
https://lore.kernel.org/all/[email protected]/
* Added Reviewed-By tags from Dexuan. Also, addressed minor comments in commit msg of both patches.
* Missed to remove check for "primary_channel->device_obj->channels_kset" in hv_create_ring_sysfs in earlier patch, as suggested by Michael. Did it now.
* Changed type for declaring bin_attrs due to changes introduced by commit 9bec944506fa ("sysfs: constify attribute_group::bin_attrs") which merged recently. Did not use bin_attrs_new since another change is in the queue to change usage of bin_attrs_new to bin_attrs (sysfs: finalize the constification of 'struct bin_attribute').
Changes since v4:
https://lore.kernel.org/all/[email protected]/
* Added Reviewed-By and Tested-By tags from Michael.
* Fixed syntax by removing extra space (addressed Greg's comment)
* Rebased to latest linux-next tip
Changes since v3:
https://lore.kernel.org/all/[email protected]/
* Addressed Michael's comments regarding handling of return value of sysfs_update_group in uio_hv_generic.
Changes since v2:
https://lore.kernel.org/all/[email protected]/
Addressed Greg's comments:
* Split the original patch into two.
* Updated the commit message to explain the problem scenario.
* Added comments for new APIs in the kerneldoc format.
* Highlighted potential race conditions and explained why sysfs should not be created in the driver probe.
* Made minor changes to how the sysfs_update_group return value is handled.
Changes since v1:
https://lore.kernel.org/all/[email protected]/
* Fixed race condition in setting channel->mmap_ring_buffer by
introducing a new variable for visibility of sysfs (addressed Greg's comments)
* Used binary attribute fields instead of regular ones for initializing attribute_group.
* Make size of ring sysfs dynamic based on actual ring buffer's size.
* Preferred to keep mmap function in uio_hv_generic to give more control over ring's mmap functionality, since this is specific to uio_hv_generic driver.
* Remove spurious warning during sysfs creation in uio_hv_generic probe.
* Added comments in a couple of places.
Changes since RFC patch:
https://lore.kernel.org/all/[email protected]/
* Different approach to solve the problem is proposed (credits to Michael Kelley).
* Core logic for sysfs creation moved out of uio_hv_generic, to VMBus drivers where rest of the sysfs attributes for a VMBus channel are defined. (addressed Greg's comments)
* Used attribute groups instead of sysfs_create* functions, and bundled ring attribute with other attributes for the channel sysfs.
Error logs:
[ 35.574120] ------------[ cut here ]------------ [ 35.574122] WARNING: CPU: 0 PID: 10 at fs/sysfs/file.c:591 sysfs_create_bin_file+0x81/0x90 [ 35.574168] Workqueue: hv_pri_chan vmbus_add_channel_work [ 35.574172] RIP: 0010:sysfs_create_bin_file+0x81/0x90 [ 35.574197] Call Trace: [ 35.574199] <TASK> [ 35.574200] ? show_regs+0x69/0x80 [ 35.574217] ? __warn+0x8d/0x130 [ 35.574220] ? sysfs_create_bin_file+0x81/0x90 [ 35.574222] ? report_bug+0x182/0x190 [ 35.574225] ? handle_bug+0x5b/0x90 [ 35.574244] ? exc_invalid_op+0x19/0x70 [ 35.574247] ? asm_exc_invalid_op+0x1b/0x20 [ 35.574252] ? sysfs_create_bin_file+0x81/0x90 [ 35.574255] hv_uio_probe+0x1e7/0x410 [uio_hv_generic] [ 35.574271] vmbus_probe+0x3b/0x90 [ 35.574275] really_probe+0xf4/0x3b0 [ 35.574279] __driver_probe_device+0x8a/0x170 [ 35.574282] driver_probe_device+0x23/0xc0 [ 35.574285] __device_attach_driver+0xb5/0x140 [ 35.574288] ? __pfx___device_attach_driver+0x10/0x10 [ 35.574291] bus_for_each_drv+0x86/0xe0 [ 35.574294] __device_attach+0xc1/0x200 [ 35.574297] device_initial_probe+0x13/0x20 [ 35.574315] bus_probe_device+0x99/0xa0 [ 35.574318] device_add+0x647/0x870 [ 35.574320] ? hrtimer_init+0x28/0x70 [ 35.574323] device_register+0x1b/0x30 [ 35.574326] vmbus_device_register+0x83/0x130 [ 35.574328] vmbus_add_channel_work+0x135/0x1a0 [ 35.574331] process_one_work+0x177/0x340 [ 35.574348] worker_thread+0x2b2/0x3c0 [ 35.574350] kthread+0xe3/0x1f0 [ 35.574353] ? __pfx_worker_thread+0x10/0x10 [ 35.574356] ? __pfx_kthread+0x10/0x10
Naman Jain (2):
uio_hv_generic: Fix sysfs creation path for ring buffer
Drivers: hv: Make the sysfs node size for the ring buffer dynamic
drivers/hv/hyperv_vmbus.h | 6 ++ drivers/hv/vmbus_drv.c | 109 ++++++++++++++++++++++++++++++++++- drivers/uio/uio_hv_generic.c | 39 ++++++------- include/linux/hyperv.h | 6 ++ 4 files changed, 137 insertions(+), 23 deletions(-)
base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e
Signature · 1 line
2.34.1
PATCH v7 1/2 uio_hv_generic: Fix sysfs creation path for ring buffer
On regular bootup, devices get registered to VMBus first, so when uio_hv_generic driver for a particular device type is probed, the device is already initialized and added, so sysfs creation in hv_uio_probe() works fine. However, when the device is removed and brought back, the channel gets rescinded and the device again gets registered to VMBus. However this time, the uio_hv_generic driver is already registered to probe for that device and in this case sysfs creation is tried before the device's kobject gets initialized completely.
Fix this by moving the core logic of sysfs creation of ring buffer, from uio_hv_generic to HyperV's VMBus driver, where the rest of the sysfs attributes for the channels are defined. While doing that, make use of attribute groups and macros, instead of creating sysfs directly, to ensure better error handling and code flow.
Problematic path:vmbus_process_offer (A new offer comes for the VMBus device)
vmbus_add_channel_work
vmbus_device_register
|-> device_register
| |...
| |-> hv_uio_probe
| |...
| |-> sysfs_create_bin_file (leads to a warning as
| the primary channel's kobject, which is used to
| create the sysfs file, is not yet initialized)
|-> kset_create_and_add
|-> vmbus_add_channel_kobj (initialization of the primary
channel's kobject happens later)Above code flow is sequential and the warning is always reproducible in this path.
--- drivers/hv/hyperv_vmbus.h | 6 +++ drivers/hv/vmbus_drv.c | 100 ++++++++++++++++++++++++++++++++++- drivers/uio/uio_hv_generic.c | 39 ++++++-------- include/linux/hyperv.h | 6 +++ 4 files changed, 128 insertions(+), 23 deletions(-)
drivers/hv/hyperv_vmbus.h +6 -0
@@ -477,4 +477,10 @@ static inline int hv_debug_add_dev_dir(struct hv_device *dev)#endif /* CONFIG_HYPERV_TESTING */ +/* Create and remove sysfs entry for memory mapped ring buffers for a channel */ +int hv_create_ring_sysfs (struct vmbus_channel *channel, +int (*hv_mmap_ring_buffer)(struct vmbus_channel *channel, +struct vm_area_struct *vma)); +int hv_remove_ring_sysfs (struct vmbus_channel *channel); +#endif /* _HYPERV_VMBUS_H */
drivers/hv/vmbus_drv.c +99 -1
126 lines not on this page · raw message
drivers/uio/uio_hv_generic.c +17 -22
@@ -131,15 +131,12 @@ static void hv_uio_rescind(struct vmbus_channel *channel)vmbus_device_unregister (channel->device_obj); } -/* Sysfs API to allow mmap of the ring buffers +/* Function used for mmap of ring buffer sysfs interface. * The ring buffer is allocated as contiguous memory by vmbus_open */ -static int hv_uio_ring_mmap (struct file *filp,struct kobject *kobj, -const struct bin_attribute *attr, -struct vm_area_struct *vma) +static int +hv_uio_ring_mmap (struct vmbus_channel *channel,struct vm_area_struct *vma) { -struct vmbus_channel *channel - = container_of(kobj, struct vmbus_channel, kobj);void *ring_buffer =page_address (channel->ringbuffer_page);if (channel->state !=CHANNEL_OPENED_STATE )
@@ -149,15 +146,6 @@ static int hv_uio_ring_mmap(struct file *filp, struct kobject *kobj, channel->ringbuffer_pagecount << PAGE_SHIFT); } -static const struct bin_attribute ring_buffer_bin_attr = { - .attr = { - .name ="ring" , - .mode =0600 , - }, - .size =2 *SZ_2M , - .mmap = hv_uio_ring_mmap, -}; -/* Callback from VMBUS subsystem when new channel created. */ static void hv_uio_new_channel (struct vmbus_channel *new_sc)
@@ -178,8 +166,7 @@ hv_uio_new_channel(struct vmbus_channel *new_sc)/* Disable interrupts on sub channel */ new_sc->inbound.ring_buffer->interrupt_mask =1 ;set_channel_read_mode (new_sc,HV_CALL_ISR ); - - ret =sysfs_create_bin_file (&new_sc->kobj, &ring_buffer_bin_attr); + ret =hv_create_ring_sysfs (new_sc, hv_uio_ring_mmap);if (ret) {dev_err (device,"sysfs create ring bin file failed; %d\n" , ret);vmbus_close (new_sc);
@@ -350,10 +337,18 @@ hv_uio_probe(struct hv_device *dev, goto fail_close; } - ret =sysfs_create_bin_file (&channel->kobj, &ring_buffer_bin_attr); -if (ret) -dev_notice (&dev->device, -"sysfs create ring bin file failed; %d\n" , ret); +/* +* This internally calls sysfs_update_group, which returns a non-zero value if it executes +* before sysfs_create_group. This is expected as the 'ring' will be created later in +* vmbus_device_register() -> vmbus_add_channel_kobj(). Thus, no need to check the return +* value and print warning. +* +* Creating/exposing sysfs in driver probe is not encouraged as it can lead to race +* conditions with userspace. For backward compatibility, "ring" sysfs could not be removed +* or decoupled from uio_hv_generic probe. Userspace programs can make use of inotify +* APIs to make sure that ring is created. +*/ +hv_create_ring_sysfs (channel, hv_uio_ring_mmap);hv_set_drvdata (dev, pdata);
@@ -375,7 +370,7 @@ hv_uio_remove(struct hv_device *dev)if (!pdata)return ; -sysfs_remove_bin_file (&dev->channel->kobj, &ring_buffer_bin_attr); +hv_remove_ring_sysfs (dev->channel);uio_unregister_device (&pdata->info);hv_uio_cleanup (dev, pdata);
include/linux/hyperv.h +6 -0
@@ -1002,6 +1002,12 @@ struct vmbus_channel {/* The max size of a packet on this channel */ u32 max_pkt_size; + +/* function to mmap ring buffer memory to the channel's sysfs ring attribute */ +int (*mmap_ring_buffer)(struct vmbus_channel *channel,struct vm_area_struct *vma); + +/* boolean to control visibility of sysfs for ring buffer */ +bool ring_sysfs_visible; };#define lock_requestor (channel, flags) \
Signature · 1 line
2.34.1
PATCH v7 2/2 Drivers: hv: Make the sysfs node size for the ring buffer dynamic
In reply to Naman JainThe ring buffer size varies across VMBus channels. The size of sysfs node for the ring buffer is currently hardcoded to 4 MB. Userspace clients either use fstat() or hardcode this size for doing mmap(). To address this, make the sysfs node size dynamic to reflect the actual ring buffer size for each channel. This will ensure that fstat() on ring sysfs node always returns the correct size of ring buffer.
--- drivers/hv/vmbus_drv.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
drivers/hv/vmbus_drv.c +10 -1
@@ -1820,7 +1820,6 @@ static struct bin_attribute chan_attr_ring_buffer = { .name = "ring", .mode = 0600, }, - .size = 2 * SZ_2M, .mmap = hv_mmap_ring_buffer_wrapper, }; static struct attribute *vmbus_chan_attrs[] = {
@@ -1880,11 +1879,21 @@ static umode_t vmbus_chan_bin_attr_is_visible(struct kobject *kobj,return attr->attr.mode; } +static size_t vmbus_chan_bin_size (struct kobject *kobj, +const struct bin_attribute *bin_attr,int a) +{ +const struct vmbus_channel *channel = + container_of(kobj, struct vmbus_channel, kobj); + +return channel->ringbuffer_pagecount <<PAGE_SHIFT ; +} +static const struct attribute_group vmbus_chan_group = { .attrs = vmbus_chan_attrs, .bin_attrs = vmbus_chan_bin_attrs, .is_visible = vmbus_chan_attr_is_visible, .is_bin_visible = vmbus_chan_bin_attr_is_visible, + .bin_size = vmbus_chan_bin_size, };static const struct kobj_type vmbus_chan_ktype = {
Signature · 1 line
2.34.1