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[bpf,v2,2/3] bpf: Enable IRQ after irq_work_raise() completes in unit_free{_rcu}()

Message ID 20230901111954.1804721-3-houtao@huaweicloud.com (mailing list archive)
State Accepted
Commit 9d7f77f997d92fa280f2a35dc0677a317c9c1acf
Delegated to: BPF
Headers show
Series bpf: Enable IRQ after irq_work_raise() completes | expand

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Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf
netdev/fixes_present fail Series targets non-next tree, but doesn't contain any Fixes tags
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1335 this patch: 1335
netdev/cc_maintainers success CCed 12 of 12 maintainers
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netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1358 this patch: 1358
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 28 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
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Commit Message

Hou Tao Sept. 1, 2023, 11:19 a.m. UTC 
From: Hou Tao <houtao1@huawei.com>

Both unit_free() and unit_free_rcu() invoke irq_work_raise() to free
freed objects back to slab and the invocation may also be preempted by
unit_alloc() and unit_alloc() may return NULL unexpectedly as shown in
the following case:

task A         task B

unit_free()
  // high_watermark = 48
  // free_cnt = 49 after free
  irq_work_raise()
    // mark irq work as IRQ_WORK_PENDING
    irq_work_claim()

               // task B preempts task A
               unit_alloc()
                 // free_cnt = 48 after alloc

               // does unit_alloc() 32-times
	       ......
	       // free_cnt = 16

	       unit_alloc()
	         // free_cnt = 15 after alloc
                 // irq work is already PENDING,
                 // so just return
                 irq_work_raise()

	       // does unit_alloc() 15-times
               ......
	       // free_cnt = 0

               unit_alloc()
                 // free_cnt = 0 before alloc
                 return NULL

Fix it by enabling IRQ after irq_work_raise() completes.

Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 kernel/bpf/memalloc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 962472ace98c..7a81dd6b1aed 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -780,11 +780,16 @@  static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
 		llist_add(llnode, &c->free_llist_extra);
 	}
 	local_dec(&c->active);
-	local_irq_restore(flags);
 
 	if (cnt > c->high_watermark)
 		/* free few objects from current cpu into global kmalloc pool */
 		irq_work_raise(c);
+	/* Enable IRQ after irq_work_raise() completes, otherwise when current
+	 * task is preempted by task which does unit_alloc(), unit_alloc() may
+	 * return NULL unexpectedly because irq work is already pending but can
+	 * not been triggered and free_llist can not be refilled timely.
+	 */
+	local_irq_restore(flags);
 }
 
 static void notrace unit_free_rcu(struct bpf_mem_cache *c, void *ptr)
@@ -802,10 +807,10 @@  static void notrace unit_free_rcu(struct bpf_mem_cache *c, void *ptr)
 		llist_add(llnode, &c->free_llist_extra_rcu);
 	}
 	local_dec(&c->active);
-	local_irq_restore(flags);
 
 	if (!atomic_read(&c->call_rcu_in_progress))
 		irq_work_raise(c);
+	local_irq_restore(flags);
 }
 
 /* Called from BPF program or from sys_bpf syscall.