| Message ID | 1405977697-1454-1-git-send-email-kamal@canonical.com |
|---|---|
| State | New |
| Headers | show |
diff --git a/fs/ubifs/shrinker.c b/fs/ubifs/shrinker.c index 9e1d056..e0a7a76 100644 --- a/fs/ubifs/shrinker.c +++ b/fs/ubifs/shrinker.c @@ -128,7 +128,6 @@ static int shrink_tnc(struct ubifs_info *c, int nr, int age, int *contention) freed = ubifs_destroy_tnc_subtree(znode); atomic_long_sub(freed, &ubifs_clean_zn_cnt); atomic_long_sub(freed, &c->clean_zn_cnt); - ubifs_assert(atomic_long_read(&c->clean_zn_cnt) >= 0); total_freed += freed; znode = zprev; }
This is a note to let you know that I have just added a patch titled UBIFS: Remove incorrect assertion in shrink_tnc() to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue This patch is scheduled to be released in version 3.8.13.27. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.8.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From e169a8f6b395f33eca9c6db8416a40dc6f689f0d Mon Sep 17 00:00:00 2001 From: hujianyang <hujianyang@huawei.com> Date: Sat, 31 May 2014 11:39:32 +0800 Subject: UBIFS: Remove incorrect assertion in shrink_tnc() commit 72abc8f4b4e8574318189886de627a2bfe6cd0da upstream. I hit the same assert failed as Dolev Raviv reported in Kernel v3.10 shows like this: [ 9641.164028] UBIFS assert failed in shrink_tnc at 131 (pid 13297) [ 9641.234078] CPU: 1 PID: 13297 Comm: mmap.test Tainted: G O 3.10.40 #1 [ 9641.234116] [<c0011a6c>] (unwind_backtrace+0x0/0x12c) from [<c000d0b0>] (show_stack+0x20/0x24) [ 9641.234137] [<c000d0b0>] (show_stack+0x20/0x24) from [<c0311134>] (dump_stack+0x20/0x28) [ 9641.234188] [<c0311134>] (dump_stack+0x20/0x28) from [<bf22425c>] (shrink_tnc_trees+0x25c/0x350 [ubifs]) [ 9641.234265] [<bf22425c>] (shrink_tnc_trees+0x25c/0x350 [ubifs]) from [<bf2245ac>] (ubifs_shrinker+0x25c/0x310 [ubifs]) [ 9641.234307] [<bf2245ac>] (ubifs_shrinker+0x25c/0x310 [ubifs]) from [<c00cdad8>] (shrink_slab+0x1d4/0x2f8) [ 9641.234327] [<c00cdad8>] (shrink_slab+0x1d4/0x2f8) from [<c00d03d0>] (do_try_to_free_pages+0x300/0x544) [ 9641.234344] [<c00d03d0>] (do_try_to_free_pages+0x300/0x544) from [<c00d0a44>] (try_to_free_pages+0x2d0/0x398) [ 9641.234363] [<c00d0a44>] (try_to_free_pages+0x2d0/0x398) from [<c00c6a60>] (__alloc_pages_nodemask+0x494/0x7e8) [ 9641.234382] [<c00c6a60>] (__alloc_pages_nodemask+0x494/0x7e8) from [<c00f62d8>] (new_slab+0x78/0x238) [ 9641.234400] [<c00f62d8>] (new_slab+0x78/0x238) from [<c031081c>] (__slab_alloc.constprop.42+0x1a4/0x50c) [ 9641.234419] [<c031081c>] (__slab_alloc.constprop.42+0x1a4/0x50c) from [<c00f80e8>] (kmem_cache_alloc_trace+0x54/0x188) [ 9641.234459] [<c00f80e8>] (kmem_cache_alloc_trace+0x54/0x188) from [<bf227908>] (do_readpage+0x168/0x468 [ubifs]) [ 9641.234553] [<bf227908>] (do_readpage+0x168/0x468 [ubifs]) from [<bf2296a0>] (ubifs_readpage+0x424/0x464 [ubifs]) [ 9641.234606] [<bf2296a0>] (ubifs_readpage+0x424/0x464 [ubifs]) from [<c00c17c0>] (filemap_fault+0x304/0x418) [ 9641.234638] [<c00c17c0>] (filemap_fault+0x304/0x418) from [<c00de694>] (__do_fault+0xd4/0x530) [ 9641.234665] [<c00de694>] (__do_fault+0xd4/0x530) from [<c00e10c0>] (handle_pte_fault+0x480/0xf54) [ 9641.234690] [<c00e10c0>] (handle_pte_fault+0x480/0xf54) from [<c00e2bf8>] (handle_mm_fault+0x140/0x184) [ 9641.234716] [<c00e2bf8>] (handle_mm_fault+0x140/0x184) from [<c0316688>] (do_page_fault+0x150/0x3ac) [ 9641.234737] [<c0316688>] (do_page_fault+0x150/0x3ac) from [<c000842c>] (do_DataAbort+0x3c/0xa0) [ 9641.234759] [<c000842c>] (do_DataAbort+0x3c/0xa0) from [<c0314e38>] (__dabt_usr+0x38/0x40) After analyzing the code, I found a condition that may cause this failed in correct operations. Thus, I think this assertion is wrong and should be removed. Suppose there are two clean znodes and one dirty znode in TNC. So the per-filesystem atomic_t @clean_zn_cnt is (2). If commit start, dirty_znode is set to COW_ZNODE in get_znodes_to_commit() in case of potentially ops on this znode. We clear COW bit and DIRTY bit in write_index() without @tnc_mutex locked. We don't increase @clean_zn_cnt in this place. As the comments in write_index() shows, if another process hold @tnc_mutex and dirty this znode after we clean it, @clean_zn_cnt would be decreased to (1). We will increase @clean_zn_cnt to (2) with @tnc_mutex locked in free_obsolete_znodes() to keep it right. If shrink_tnc() performs between decrease and increase, it will release other 2 clean znodes it holds and found @clean_zn_cnt is less than zero (1 - 2 = -1), then hit the assertion. Because free_obsolete_znodes() will soon correct @clean_zn_cnt and no harm to fs in this case, I think this assertion could be removed. 2 clean zondes and 1 dirty znode, @clean_zn_cnt == 2 Thread A (commit) Thread B (write or others) Thread C (shrinker) ->write_index ->clear_bit(DIRTY_NODE) ->clear_bit(COW_ZNODE) @clean_zn_cnt == 2 ->mutex_locked(&tnc_mutex) ->dirty_cow_znode ->!ubifs_zn_cow(znode) ->!test_and_set_bit(DIRTY_NODE) ->atomic_dec(&clean_zn_cnt) ->mutex_unlocked(&tnc_mutex) @clean_zn_cnt == 1 ->mutex_locked(&tnc_mutex) ->shrink_tnc ->destroy_tnc_subtree ->atomic_sub(&clean_zn_cnt, 2) ->ubifs_assert <- hit ->mutex_unlocked(&tnc_mutex) @clean_zn_cnt == -1 ->mutex_lock(&tnc_mutex) ->free_obsolete_znodes ->atomic_inc(&clean_zn_cnt) ->mutux_unlock(&tnc_mutex) @clean_zn_cnt == 0 (correct after shrink) Signed-off-by: hujianyang <hujianyang@huawei.com> Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- fs/ubifs/shrinker.c | 1 - 1 file changed, 1 deletion(-) -- 1.9.1