Messages in this thread | | | Date | Wed, 5 Feb 2014 14:58:37 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH v3] slub: fix false-positive lockdep warning in free_partial() |
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On Wed, Feb 05, 2014 at 12:15:33PM +0400, Vladimir Davydov wrote: > Commit c65c1877bd68 ("slub: use lockdep_assert_held") requires > remove_partial() to be called with n->list_lock held, but free_partial() > called from kmem_cache_close() on cache destruction does not follow this > rule, leading to a warning: > > WARNING: CPU: 0 PID: 2787 at mm/slub.c:1536 __kmem_cache_shutdown+0x1b2/0x1f0() > Modules linked in: > CPU: 0 PID: 2787 Comm: modprobe Tainted: G W 3.14.0-rc1-mm1+ #1 > Hardware name: > 0000000000000600 ffff88003ae1dde8 ffffffff816d9583 0000000000000600 > 0000000000000000 ffff88003ae1de28 ffffffff8107c107 0000000000000000 > ffff880037ab2b00 ffff88007c240d30 ffffea0001ee5280 ffffea0001ee52a0 > Call Trace: > [<ffffffff816d9583>] dump_stack+0x51/0x6e > [<ffffffff8107c107>] warn_slowpath_common+0x87/0xb0 > [<ffffffff8107c145>] warn_slowpath_null+0x15/0x20 > [<ffffffff811c7fe2>] __kmem_cache_shutdown+0x1b2/0x1f0 > [<ffffffff811908d3>] kmem_cache_destroy+0x43/0xf0 > [<ffffffffa013a123>] xfs_destroy_zones+0x103/0x110 [xfs] > [<ffffffffa0192b54>] exit_xfs_fs+0x38/0x4e4 [xfs] > [<ffffffff811036fa>] SyS_delete_module+0x19a/0x1f0 > [<ffffffff816dfcd8>] ? retint_swapgs+0x13/0x1b > [<ffffffff810d2125>] ? trace_hardirqs_on_caller+0x105/0x1d0 > [<ffffffff81359efe>] ? trace_hardirqs_on_thunk+0x3a/0x3f > [<ffffffff816e8539>] system_call_fastpath+0x16/0x1b > > Although this cannot actually result in a race, because on cache > destruction there should not be any concurrent frees or allocations from > the cache, let's add spin_lock/unlock to free_partial() just to keep > lockdep happy.
Really? We are adding a spin lock for a case where it is not needed just to quiet lockdep?
Now if it really isn't needed, then why don't we do the following instead of adding the overhead of taking a lock?
static inline __remove_partial(struct kmem_cache_node *n, struct page *page) { list_del(&page->lru); n->nr_partial--; }
static inline remove_partial(struct kmem_cache_node *n, struct page *page) { lockdep_assert_held(&n->list_lock); __remove_partial(n, page); }
And then just call __remove_partial() where we don't need to check if the lock is held or not with a big comment to it.
That, IMNSHO, is a much better solution.
-- Steve
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