Re: [PATCH] module: print module name on refcount error
From: Luis Chamberlain <mcgrof@kernel.org>
Date: 2023-06-30 23:05:43
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On Mon, Jun 26, 2023 at 12:32:52PM +0200, Jean Delvare wrote:
quoted hunk ↗ jump to hunk
If module_put() triggers a refcount error, include the culprit module name in the warning message, to easy further investigation of the issue. Signed-off-by: Jean Delvare <redacted> Suggested-by: Michal Hocko <mhocko@suse.com> Cc: Luis Chamberlain <mcgrof@kernel.org> --- kernel/module/main.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)--- linux-6.3.orig/kernel/module/main.c +++ linux-6.3/kernel/module/main.c@@ -850,7 +850,9 @@ void module_put(struct module *module) if (module) { preempt_disable(); ret = atomic_dec_if_positive(&module->refcnt); - WARN_ON(ret < 0); /* Failed to put refcount */ + WARN(ret < 0, + KERN_WARNING "Failed to put refcount for module %s\n", + module->name); trace_module_put(module, _RET_IP_); preempt_enable(); }
The mod struct ends up actually being allocated, we first read the ELF passed by userspace and we end up allocating space for struct module when reading the ELF section ".gnu.linkonce.this_module". We cache the ELF section index in info->index.mod, we finally copy the module into the allocated space with move_module(). In linux-next code this is much more clear now. What prevents us from racing to free the module and thus invalidating the name? For instance the system call to delete_module() could hammer and so have tons of threads racing try_stop_module(), eventually one of them could win and free_module() would kick in gear. What prevents code from racing the free with a random module_put() called by some other piece of code? I realize this may implicate even the existing code seems racy. Luis