From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f71.google.com (mail-pl0-f71.google.com [209.85.160.71]) by kanga.kvack.org (Postfix) with ESMTP id 875D46B0007 for ; Mon, 5 Feb 2018 19:49:22 -0500 (EST) Received: by mail-pl0-f71.google.com with SMTP id f4so325197plr.14 for ; Mon, 05 Feb 2018 16:49:22 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id w25sor460147pfk.134.2018.02.05.16.49.21 for (Google Transport Security); Mon, 05 Feb 2018 16:49:21 -0800 (PST) From: Joel Fernandes Subject: [PATCH RFC] ashmem: Fix lockdep RECLAIM_FS false positive Date: Mon, 5 Feb 2018 16:49:03 -0800 Message-Id: <20180206004903.224390-1-joelaf@google.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org Cc: Joel Fernandes , Peter Zilstra , mhocko@kernel.org, minchan@kernel.org, linux-mm@kvack.org During invocation of ashmem shrinker under memory pressure, ashmem calls into VFS code via vfs_fallocate. We however make sure we don't enter it if the allocation was GFP_FS to prevent looping into filesystem code. However lockdep doesn't know this and prints a lockdep splat as below. This patch fixes the issue by releasing the reclaim_fs lock after checking for GFP_FS but before calling into the VFS path, and reacquiring it after so that lockdep can continue reporting any reclaim issues later. [ 2115.359650] -(1)[106:kswapd0]================================= [ 2115.359665] -(1)[106:kswapd0][ INFO: inconsistent lock state ] [ 2115.359684] -(1)[106:kswapd0]4.9.60+ #2 Tainted: G W O [ 2115.359699] -(1)[106:kswapd0]--------------------------------- [ 2115.359715] -(1)[106:kswapd0]inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage. [ 2115.359732] -(1)[106:kswapd0]kswapd0/106 [HC0[0]:SC0[0]:HE1:SE1] takes: [ 2115.359748] (&sb->s_type->i_mutex_key#9){++++?+}, at: [] shmem_fallocate+0x104/0x880 [ 2115.359809] -(1)[106:kswapd0]{RECLAIM_FS-ON-W} state was registered at: [ 2115.359828] -(1)[106:kswapd0] mark_lock+0x2a4/0x10c0 [ 2115.359845] -(1)[106:kswapd0] mark_held_locks+0xc0/0x128 [ 2115.359862] -(1)[106:kswapd0] lockdep_trace_alloc+0x284/0x368 [ 2115.359881] -(1)[106:kswapd0] kmem_cache_alloc+0x3c/0x368 [ 2115.359900] -(1)[106:kswapd0] __d_alloc+0x3c/0x7a8 [ 2115.359917] -(1)[106:kswapd0] d_alloc+0x34/0x140 [ 2115.359934] -(1)[106:kswapd0] d_alloc_parallel+0xfc/0x1480 [ 2115.359953] -(1)[106:kswapd0] lookup_open+0x3c4/0x12a8 [ 2115.359971] -(1)[106:kswapd0] path_openat+0xb40/0x1dc0 [ 2115.359987] -(1)[106:kswapd0] do_filp_open+0x170/0x258 [ 2115.360006] -(1)[106:kswapd0] do_sys_open+0x1b8/0x2f0 [ 2115.360023] -(1)[106:kswapd0] SyS_openat+0x10/0x18 [ 2115.360041] -(1)[106:kswapd0] el0_svc_naked+0x24/0x28 [ 2115.360056] -(1)[106:kswapd0]irq event stamp: 2437365 [ 2115.360079] -(1)[106:kswapd0]hardirqs last enabled at (2437365): [] mutex_trylock+0x224/0x460 [ 2115.360098] -(1)[106:kswapd0]hardirqs last disabled at (2437364): [] mutex_trylock+0xe8/0x460 [ 2115.360116] -(1)[106:kswapd0]softirqs last enabled at (2436534): [] __do_softirq+0xc38/0x1190 [ 2115.360138] -(1)[106:kswapd0]softirqs last disabled at (2436515): [] irq_exit+0x1ac/0x228 [ 2115.360153] -(1)[106:kswapd0]\x0aother info that might help us debug this: [ 2115.360169] -(1)[106:kswapd0] Possible unsafe locking scenario:\x0a [ 2115.360184] -(1)[106:kswapd0] CPU0 [ 2115.360198] -(1)[106:kswapd0] ---- [ 2115.360211] -(1)[106:kswapd0] lock(&sb->s_type->i_mutex_key#9); [ 2115.360252] -(1)[106:kswapd0] [ 2115.360265] -(1)[106:kswapd0] lock(&sb->s_type->i_mutex_key#9); [ 2115.360304] -(1)[106:kswapd0]\x0a *** DEADLOCK ***\x0a [ 2115.360322] -(1)[106:kswapd0] #0: (shrinker_rwsem){++++..}, at: [] shrink_slab.part.15.constprop.28+0xb0/0xe10 [ 2115.360382] -(1)[106:kswapd0] #1: (ashmem_mutex){+.+.+.}, at: [] ashmem_shrink_scan+0x80/0x308 [ 2115.360439] -(1)[106:kswapd0]\x0astack backtrace: [ 2115.360462] -(1)[106:kswapd0]CPU: 1 PID: 106 Comm: kswapd0 Tainted: G W O 4.9.60+ #2 [ 2115.360478] -(1)[106:kswapd0]Hardware name: MT6765 (DT) [ 2115.360494] -(1)[106:kswapd0]Call trace: [ 2115.360515] -(1)[106:kswapd0][] dump_backtrace+0x0/0x400 [ 2115.360533] -(1)[106:kswapd0][] show_stack+0x14/0x20 [ 2115.360555] -(1)[106:kswapd0][] dump_stack+0xb0/0xe8 [ 2115.360576] -(1)[106:kswapd0][] print_usage_bug.part.24+0x548/0x568 [ 2115.360595] -(1)[106:kswapd0][] mark_lock+0x494/0x10c0 [ 2115.360613] -(1)[106:kswapd0][] __lock_acquire+0xc94/0x58e8 [ 2115.360630] -(1)[106:kswapd0][] lock_acquire+0x1d0/0x708 [ 2115.360650] -(1)[106:kswapd0][] down_write+0x48/0xd0 [ 2115.360669] -(1)[106:kswapd0][] shmem_fallocate+0x104/0x880 [ 2115.360688] -(1)[106:kswapd0][] ashmem_shrink_scan+0x1a4/0x308 [ 2115.360709] -(1)[106:kswapd0][] shrink_slab.part.15.constprop.28+0x330/0xe10 [ 2115.360729] -(1)[106:kswapd0][] shrink_node+0x1b4/0x588 [ 2115.360747] -(1)[106:kswapd0][] kswapd+0x774/0x1640 [ 2115.360767] -(1)[106:kswapd0][] kthread+0x28c/0x310 [ 2115.360786] -(1)[106:kswapd0][] ret_from_fork+0x10/0x50 Cc: Peter Zilstra Cc: mhocko@kernel.org Cc: minchan@kernel.org Cc: linux-mm@kvack.org Signed-off-by: Joel Fernandes --- drivers/staging/android/ashmem.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index 372ce9913e6d..7e060f32aaa8 100644 --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -32,6 +32,7 @@ #include #include #include +#include #include "ashmem.h" #define ASHMEM_NAME_PREFIX "dev/ashmem/" @@ -446,8 +447,17 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) if (!(sc->gfp_mask & __GFP_FS)) return SHRINK_STOP; - if (!mutex_trylock(&ashmem_mutex)) + /* + * Release reclaim-fs marking since we've already checked GFP_FS, This + * will prevent lockdep's reclaim recursion deadlock false positives. + * We'll renable it before returning from this function. + */ + fs_reclaim_release(sc->gfp_mask); + + if (!mutex_trylock(&ashmem_mutex)) { + fs_reclaim_acquire(sc->gfp_mask); return -1; + } list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) { loff_t start = range->pgstart * PAGE_SIZE; @@ -464,6 +474,8 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) break; } mutex_unlock(&ashmem_mutex); + + fs_reclaim_acquire(sc->gfp_mask); return freed; } -- 2.16.0.rc1.238.g530d649a79-goog -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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