On Sat, Dec 25, 2021 at 11:27:04PM +0800, kernel test robot wrote: > tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git dev > branch HEAD: cc5fef71a1c741473eebb1aa6f7056ceb49bc33d ext4: replace snprintf in show functions with sysfs_emit > > Error/Warning reports: > > https://lore.kernel.org/linux-ext4/202112101722.3Kpomg0h-lkp@xxxxxxxxx > > possible Error/Warning in current branch (please contact us if interested): > > fs/ext4/super.c:2640:22-40: ERROR: reference preceded by free on line 2639 The Intel test robot mis-identified the commit which introduced this problem (it looks like the first commit with the problem is commit e6e268cb6822 ("ext4: move quota configuration out of handle_mount_opt()"), but it caused me to take a closer look, and this looks... wrong. >From ext4_apply_quota_options() in fs/extr4/super.c: qname = ctx->s_qf_names[i]; /* May be NULL */ ctx->s_qf_names[i] = NULL; kfree(sbi->s_qf_names[i]); rcu_assign_pointer(sbi->s_qf_names[i], qname); set_opt(sb, QUOTA); sbi->s_qf_names[i] is an RCU protected pointer, which is used via rcu_derference(). So how can it be safe to kfree() the pointer; should that be kfree_rcu() at the very least? Lukas, can you take a look and let me know? Thanks! - Ted
