On Fri, Oct 27, 2023, at 13:47, Naresh Kamboju wrote:
Following kernel crash noticed on x86_64 while running selftests ftracetests running 6.6.0-rc7-next-20231026.
Reported-by: Linux Kernel Functional Testing lkft@linaro.org
My guess would be that this is caused by 5790b1fb3d67 ("eventfs: Remove eventfs_file and just use eventfs_inode"), in which Steven Rostedt recently added the create_dir_dentry() function through a rewrite:
log:
# ok 44 ftrace - test for function traceon/off triggers # ok 45 ftrace - test tracing error log support # ok 46 Test creation and deletion of trace instances while setting an event [ 1402.419605] BUG: kernel NULL pointer dereference, address: 0000000000000097 [ 1402.426574] #PF: supervisor read access in kernel mode
...
[ 1402.581170] ? exc_page_fault (arch/x86/include/asm/irqflags.h:26 arch/x86/include/asm/irqflags.h:67 arch/x86/include/asm/irqflags.h:127 arch/x86/mm/fault.c:1513 arch/x86/mm/fault.c:1561) [ 1402.585094] ? asm_exc_page_fault (arch/x86/include/asm/idtentry.h:570) [ 1402.589283] ? __lock_acquire (kernel/locking/lockdep.c:5005) [ 1402.593296] ? lock_acquire (kernel/locking/lockdep.c:467 (discriminator 4) kernel/locking/lockdep.c:5755 (discriminator 4) kernel/locking/lockdep.c:5718 (discriminator 4))
The lock passed to spin_lock() and lock_acquire() is a NULL pointer.
[ 1402.597045] ? create_dir_dentry.part.0 (fs/tracefs/event_inode.c:357 (discriminator 1)) [ 1402.601928] lock_acquire (kernel/locking/lockdep.c:467 (discriminator 4) kernel/locking/lockdep.c:5755 (discriminator 4) kernel/locking/lockdep.c:5718 (discriminator 4)) [ 1402.605503] ? d_invalidate (fs/dcache.c:1725 (discriminator 1))
This lock is part of the dentry passed to d_invalidate()
[ 1402.609170] ? lock_release (kernel/locking/lockdep.c:5429 kernel/locking/lockdep.c:5773) [ 1402.612923] ? create_dir_dentry.part.0 (fs/tracefs/event_inode.c:387) [ 1402.617803] _raw_spin_lock (include/linux/spinlock_api_smp.h:134 kernel/locking/spinlock.c:154) [ 1402.621467] ? d_invalidate (fs/dcache.c:1725 (discriminator 1)) [ 1402.625126] d_invalidate (fs/dcache.c:1725 (discriminator 1)) [ 1402.628619] create_dir_dentry.part.0 (fs/tracefs/event_inode.c:390)
Which is called by create_dir_dentry(). I don't see a bug in that function, but maybe Steve has an idea.
Arnd