I included a patch , not like it's needed . Recently I've been
evaluating likely/unlikely branch prediction .. One thing that I found
is that the kfree function is often called with a NULL "objp" . In fact
it's so frequent that the "unlikely" branch predictor should be inverted!
Or at least on my configuration.
Here are some examples of the warnings that I observed ..
printk: 66 messages suppressed.
BUG: warning at mm/slab.c:3384/kfree()
<c01043d3> show_trace+0x13/0x20 <c01043fe> dump_stack+0x1e/0x20
<c015e334> kfree+0xa4/0xc0 <c032584b> make_request+0x36b/0x670
<c0210305> generic_make_request+0x175/0x240 <c02107d7> submit_bio+0x57/0x100
<c01648f6> submit_bh+0x106/0x160 <c0165a62> __block_write_full_page+0x222/0x3f0
<c0165d28> block_write_full_page+0xf8/0x100 <c016a4b1> blkdev_writepage+0x21/0x30
<c0188c1e> mpage_writepages+0x1ae/0x3d0 <c016a46e> generic_writepages+0x1e/0x20
<c0148f9d> do_writepages+0x2d/0x50 <c0186b70> __writeback_single_inode+0xa0/0x400
<c018716b> sync_sb_inodes+0x1bb/0x2a0 <c01877bf> writeback_inodes+0xaf/0xe5
<c0148d53> wb_kupdate+0x83/0x100 <c0149ab2> pdflush+0x102/0x1c0
<c0131fa4> kthread+0xc4/0xf0 <c0100ed5> kernel_thread_helper+0x5/0x10
printk: 157 messages suppressed.
BUG: warning at mm/slab.c:3384/kfree()
<c01043d3> show_trace+0x13/0x20 <c01043fe> dump_stack+0x1e/0x20
<c015e334> kfree+0xa4/0xc0 <c0140405> audit_syscall_exit+0x405/0x430
<c0106a56> do_syscall_trace+0x1d6/0x245 <c010320a> syscall_exit_work+0x16/0x1c
Daniel
Index: linux-2.6.16/mm/slab.c
===================================================================
--- linux-2.6.16.orig/mm/slab.c
+++ linux-2.6.16/mm/slab.c
@@ -3380,8 +3380,10 @@ void kfree(const void *objp)
struct kmem_cache *c;
unsigned long flags;
- if (unlikely(!objp))
+ if (unlikely(!objp)){
+ WARN_ON(printk_ratelimit());
return;
+ }
local_irq_save(flags);
kfree_debugcheck(objp);
c = virt_to_cache(objp);
-
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