On Thu, Aug 15, 2019 at 05:09:45PM -0700, Scott Branden wrote:
A race condition exists between _request_firmware_prepare checking if firmware is assigned and firmware_fallback_sysfs creating a sysfs entry (kernel trace below). To avoid such condition add a mutex fw_lock_fallback to protect against such condition.
I am not buying this fix, and it seems sloppy. More below.
misc test_firmware: Falling back to sysfs fallback for: nope-test-firmware.bin
So the fallback kicks in with the file that is not there.
sysfs: cannot create duplicate filename '/devices/virtual/misc/test_firmware/nope-test-firmware.bin'
And we have a duplicate entry, for the *device* created to allow us to create a file entry to allow us to copy the file. Your tests had a loop, so there is actually a race between two entries being created while one one failed.
CPU: 4 PID: 2059 Comm: test_firmware-3 Not tainted 5.3.0-rc4 #1 Hardware name: Dell Inc. OptiPlex 7010/0KRC95, BIOS A13 03/25/2013 Call Trace: dump_stack+0x67/0x90 sysfs_warn_dup.cold+0x17/0x24 sysfs_create_dir_ns+0xb3/0xd0 kobject_add_internal+0xa6/0x2a0 kobject_add+0x7e/0xb0
Note: kobject_add().
? _cond_resched+0x15/0x30 device_add+0x121/0x670 firmware_fallback_sysfs+0x15c/0x3c9 _request_firmware+0x432/0x5a0 ? devres_find+0x63/0xc0 request_firmware_into_buf+0x63/0x80 test_fw_run_batch_request+0x96/0xe0 kthread+0xfb/0x130 ? reset_store+0x30/0x30 ? kthread_park+0x80/0x80 ret_from_fork+0x3a/0x50 kobject_add_internal failed for nope-test-firmware.bin with -EEXIST, don't try to register things with the same name in the same directory.
So above it makes it even clearer, two kobjets with the same name.
Signed-off-by: Scott Branden scott.branden@broadcom.com
drivers/base/firmware_loader/main.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c index bf44c79beae9..ce9896e3b782 100644 --- a/drivers/base/firmware_loader/main.c +++ b/drivers/base/firmware_loader/main.c @@ -88,6 +88,7 @@ static inline struct fw_priv *to_fw_priv(struct kref *ref) /* fw_lock could be moved to 'struct fw_sysfs' but since it is just
- guarding for corner cases a global lock should be OK */
DEFINE_MUTEX(fw_lock); +DEFINE_MUTEX(fw_lock_fallback);
The reason I don't like this fix is that this mutex is named after ther fallback interface... but...
static struct firmware_cache fw_cache; @@ -758,6 +759,17 @@ _request_firmware(const struct firmware **firmware_p, const char *name, if (!firmware_p) return -EINVAL;
- /*
* There is a race condition between _request_firmware_prepare checking* if firmware is assigned and firmware_fallback_sysfs creating sysfs* entries with duplicate names.* Yet, with this lock the firmware_test locks up with cache enabled* and no event used during firmware test.* This points to some very racy code I don't know how to entirely fix.*/- if (opt_flags & FW_OPT_NOCACHE)
mutex_lock(&fw_lock_fallback);
Whoa.. What does no-cache have anything to do with the fallback interface other than the fact we enable this feature for the fallback interface? We don't need to penalize non-fallback users who *also* may want to enable the no-cache feature.
So, the fix should be within the boundaries of the creation / deletion of the kobject, not this nocache feature. Can you please re-evaluate this code and look for a more compartamentalized solution to the fallback code only?
Luis