Messages in this thread Patch in this message | | | From | Rusty Russell <> | Subject | Re: [Regression] Crash in load_module() while freeing args | Date | Wed, 26 May 2010 21:27:24 +0930 |
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On Wed, 26 May 2010 05:30:58 pm Rusty Russell wrote: > On Wed, 26 May 2010 09:17:32 am Linus Torvalds wrote: > > > > On Wed, 26 May 2010, Rafael J. Wysocki wrote: > > > > > > I'm not able to reproduce the issue with the following commit reverted: > > > > > > commit 480b02df3aa9f07d1c7df0cd8be7a5ca73893455 > > > Author: Rusty Russell <rusty@rustcorp.com.au> > > > Date: Wed May 19 17:33:39 2010 -0600 > > > > > > module: drop the lock while waiting for module to complete initialization. > > > > Hmm. That does seem to be buggy. We can't just drop and re-take the lock: > > that may make sense _internally_ as far as resolve_symbol() itself is > > concerned, but the caller will its own local variables, and some of those > > will no longer be valid if the lock was dropped. > > Well, yes, obviously I missed something :( I'll look at it tonight after > Arabella is asleep.
See if you can spot it (I acked the patch, so I can't point fingers):
free_core: module_free(mod, mod->module_core); /* mod will be freed with core. Don't access it beyond this line! */ free_percpu: percpu_modfree(mod);
Only a year after Masami fixed that and added the comment, too :(
I suspect that the increased parallelism enabled by this patch uncovered this bug. Does this fix it?
(Side note: the locking should be simplified. No code before simplify_symbols actually needs the lock, so we should grab it just for that, then again at the end. We use kobjects to protect us from multiple loads as a side-effect, but we should move that registration to the end).
Subject: module: fix reference to mod->percpu after freeing module.
The comment about the mod being freed is self-explanatory, but neither Tejun nor I read it. This bug was introduced in 259354deaa, after it had previously been fixed in 6e2b75740b. How embarrassing.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Tejun Heo <tj@kernel.org> Cc: Masami Hiramatsu <mhiramat@redhat.com>
diff --git a/kernel/module.c b/kernel/module.c --- a/kernel/module.c +++ b/kernel/module.c @@ -2031,6 +2031,7 @@ static noinline struct module *load_modu long err = 0; void *ptr = NULL; /* Stops spurious gcc warning */ unsigned long symoffs, stroffs, *strmap; + void __percpu *percpu; mm_segment_t old_fs; @@ -2175,6 +2176,8 @@ static noinline struct module *load_modu goto free_mod; sechdrs[pcpuindex].sh_flags &= ~(unsigned long)SHF_ALLOC; } + /* Keep this around for failure path. */ + percpu = mod_percpu(mod); /* Determine total sizes, and put offsets in sh_entsize. For now this is done generically; there doesn't appear to be any @@ -2480,7 +2483,7 @@ static noinline struct module *load_modu module_free(mod, mod->module_core); /* mod will be freed with core. Don't access it beyond this line! */ free_percpu: - percpu_modfree(mod); + free_percpu(percpu); free_mod: kfree(args); kfree(strmap);
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