From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from invmail3.skhynix.com (exvmail3.hynix.com [166.125.252.90]) by smtp.subspace.kernel.org (Postfix) with ESMTP id A4CC733985 for ; Fri, 28 Mar 2025 07:25:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=166.125.252.90 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743146740; cv=none; b=E+WLdoXltfymm3BRKv0VxZNqQwvApQfUYkJ4nu3xIgD9cXdaRSzcZkxegSt0S0wGVilyZ0klk5eAfJiuwfhbwGQE6wpKRZl7FJM8ty0DV5/gwn1CWeBicPd3ytbihXLbs/0BBvw+QMXHTZnxjZpBtQ/EYcK8m2vXfWFro7QMjUQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743146740; c=relaxed/simple; bh=XfN/P0HLGm+9+5UWH4llncDKNWXDdPWHvgJfUOR4cm0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=MK0P/dFQOoJRzrslybiAiFEFTGaZHySF7IiyRJf3C7fTd4kzKQvQsBMnESbzkYenc6TrqsSJjGoCugZM5LoYbDTojnQTvrHMEIvz29Y7+uhJDlKP2wzYoXUgPcZgBg1jCpymA9u1PKzcCjNvdcpnMk3fGC9Kl+PhG9jiiVyKmIM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sk.com; spf=pass smtp.mailfrom=sk.com; arc=none smtp.client-ip=166.125.252.90 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sk.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sk.com X-AuditID: a67dfc59-03fff7000000aab6-c6-67e64eeb4151 From: "yohan.joung" To: linux-f2fs-devel@lists.sourceforge.net Cc: chao@kernel.org, jaegeuk@kernel.org, jyh429@gmail.com, linux-kernel@vger.kernel.org, pilhyun.kim@sk.com, yohan.joung@sk.com Subject: [External Mail] Re: [f2fs-dev] [External Mail] Re: [External Mail] Re: [PATCH] f2fs: prevent the current section from being selected as a victim during garbage collection Date: Fri, 28 Mar 2025 16:25:26 +0900 Message-ID: <20250328072530.2475-1-yohan.joung@sk.com> X-Mailer: git-send-email 2.49.0.windows.1 In-Reply-To: <3a2149b5-68b7-413d-8098-27ee5049f146@kernel.org> References: <3a2149b5-68b7-413d-8098-27ee5049f146@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFjrJLMWRmVeSWpSXmKPExsXC9ZZnke5rv2fpBgdvmVmcnnqWyeLJ+lnM Fl+uXmO3uLTI3eLyrjlsDqweO2fdZffYtKqTzWP3gs9MHp83yQWwRHHZpKTmZJalFunbJXBl rDg7lbngqkfFih2vmBsYJ1h0MXJwSAiYSMxc4NHFyAlhrjrBDGKzCWhI/OntBbNFBLQkJjb8 Zexi5OJgFuhklFh/8DMriCMssJlR4u/riWBVLAKqEvd3rWcFsXkFzCRmTT3AAjFVU2LHl/NM IDangJ3EgVXLwGqEBGwlZpz8xA5RLyhxcuYTFpCDmAXUJdbPEwIJMwvISzRvnc0MsktCYAGb xL7Wh4wQMyUlDq64wTKBUWAWkvZZCO2zkLQvYGRexSiSmVeWm5iZY6xXnJ1RmZdZoZecn7uJ ERjAy2r/RO5g/HYh+BCjAAejEg/vAdun6UKsiWXFlbmHGCU4mJVEeCWvPEkX4k1JrKxKLcqP LyrNSS0+xCjNwaIkzmv0rTxFSCA9sSQ1OzW1ILUIJsvEwSnVwBhev/HVv88F/1/tvlkjoH5Q /kiSYLiUjbSiqpMiV2LBqWM62rOuddmrFsaUdHIv2fzXN2RVuIF27adt5avnuhyVDQjISI2x PLB357fCVItpjz58KtgnvZXXaduuuF1T20K6F/JcnjPv1JtVXk8F3l3kvqBp5FgY8d7n8+WX MnO+9L/ROnJtupkSS3FGoqEWc1FxIgApyegSXAIAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrMLMWRmVeSWpSXmKPExsXCNUNlju5rv2fpBodXalmcnnqWyeLJ+lnM Fl+uXmO3uLTI3eLyrjlsFhPmXmWyeL/1HqMDu8fOWXfZPTat6mTz2L3gM5PHt9seHp83yQWw RnHZpKTmZJalFunbJXBlrDg7lbngqkfFih2vmBsYJ1h0MXJySAiYSMxcdYIZxGYT0JD409sL ZosIaElMbPjL2MXIxcEs0Mkosf7gZ1YQR1hgM6PE39cTwapYBFQl7u9azwpi8wqYScyaeoAF YqqmxI4v55lAbE4BO4kDq5aB1QgJ2ErMOPmJHaJeUOLkzCdA9RxAG9Ql1s8TAgkzC8hLNG+d zTyBkXcWkqpZCFWzkFQtYGRexSiSmVeWm5iZY6ZXnJ1RmZdZoZecn7uJERiUy2r/TNrB+O2y +yFGAQ5GJR7eA7ZP04VYE8uKK3MPMUpwMCuJ8EpeeZIuxJuSWFmVWpQfX1Sak1p8iFGag0VJ nNcrPDVBSCA9sSQ1OzW1ILUIJsvEwSnVwOhhtHzTqlOZbisUvEuubXk2k0VQLjC//1jMwnPr HwdPep34vN9z2zT7C/ZLow8e9k8yUFx77VXaoiipu3mJKVZPv71cfXC94uu/mq1XpFZMmZO4 5dONU3d8n+6S5UwvaCxqO8x31W1Fh+SEhNi5DH/Kppsbvb8ziz/ZRlpFv179lIAaa79HuasS S3FGoqEWc1FxIgDi17SZRgIAAA== X-CFilter-Loop: Reflected > On 2025/3/28 11:40, yohan.joung wrote: > >> From: Chao Yu > >> Sent: Thursday, March 27, 2025 10:48 PM > >> To: 정요한(JOUNG YOHAN) Mobile AE ; Yohan Joung > >> ; jaegeuk@kernel.org; daeho43@gmail.com > >> Cc: chao@kernel.org; linux-f2fs-devel@lists.sourceforge.net; linux- > >> kernel@vger.kernel.org; 김필현(KIM PILHYUN) Mobile AE > >> > >> Subject: [External Mail] Re: [External Mail] Re: [External Mail] Re: > >> [PATCH] f2fs: prevent the current section from being selected as a > >> victim during garbage collection > >> > >> On 2025/3/27 16:00, yohan.joung@sk.com wrote: > >>>> From: Chao Yu > >>>> Sent: Thursday, March 27, 2025 4:30 PM > >>>> To: 정요한(JOUNG YOHAN) Mobile AE ; Yohan Joung > >>>> ; jaegeuk@kernel.org; daeho43@gmail.com > >>>> Cc: chao@kernel.org; linux-f2fs-devel@lists.sourceforge.net; linux- > >>>> kernel@vger.kernel.org; 김필현(KIM PILHYUN) Mobile AE > >>>> > >>>> Subject: [External Mail] Re: [External Mail] Re: [PATCH] f2fs: > >>>> prevent the current section from being selected as a victim during > >>>> garbage collection > >>>> > >>>> On 3/27/25 14:43, yohan.joung@sk.com wrote: > >>>>>> From: Chao Yu > >>>>>> Sent: Thursday, March 27, 2025 3:02 PM > >>>>>> To: Yohan Joung ; jaegeuk@kernel.org; > >>>>>> daeho43@gmail.com > >>>>>> Cc: chao@kernel.org; linux-f2fs-devel@lists.sourceforge.net; > >>>>>> linux- kernel@vger.kernel.org; 정요한(JOUNG YOHAN) Mobile AE > >>>>>> > >>>>>> Subject: [External Mail] Re: [PATCH] f2fs: prevent the current > >>>>>> section from being selected as a victim during garbage collection > >>>>>> > >>>>>> On 3/26/25 22:14, Yohan Joung wrote: > >>>>>>> When selecting a victim using next_victim_seg in a large > >>>>>>> section, the selected section might already have been cleared > >>>>>>> and designated as the new current section, making it actively in > use. > >>>>>>> This behavior causes inconsistency between the SIT and SSA. > >>>>>> > >>>>>> Hi, does this fix your issue? > >>>>> > >>>>> This is an issue that arises when dividing a large section into > >>>>> segments for garbage collection. > >>>>> caused by the background GC (garbage collection) thread in large > >>>>> section > >>>>> f2fs_gc(victim_section) -> > >>>>> f2fs_clear_prefree_segments(victim_section)-> > >>>>> cursec(victim_section) -> f2fs_gc(victim_section by > >>>>> next_victim_seg) > >>>> > >>>> I didn't get it, why f2fs_get_victim() will return section which is > >>>> used by curseg? It should be avoided by checking w/ sec_usage_check(). > >>>> > >>>> Or we missed to check gcing section which next_victim_seg points to > >>>> during get_new_segment()? > >>>> > >>>> Can this happen? > >>>> > >>>> e.g. > >>>> - bggc selects sec #0 > >>>> - next_victim_seg: seg #0 > >>>> - migrate seg #0 and stop > >>>> - next_victim_seg: seg #1 > >>>> - checkpoint, set sec #0 free if sec #0 has no valid blocks > >>>> - allocate seg #0 in sec #0 for curseg > >>>> - curseg moves to seg #1 after allocation > >>>> - bggc tries to migrate seg #1 > >>>> > >>>> Thanks, > >>> That's correct > >>> In f2fs_get_victim, we use next_victim_seg to directly jump to > >>> got_result, thereby bypassing sec_usage_check What do you think > >>> about this change? > >>> > >>> @@ -850,15 +850,20 @@ int f2fs_get_victim(struct f2fs_sb_info *sbi, > >> unsigned int *result, > >>> p.min_segno = sbi->next_victim_seg[BG_GC]; > >>> *result = p.min_segno; > >>> sbi->next_victim_seg[BG_GC] = NULL_SEGNO; > >>> - goto got_result; > >>> } > >>> if (gc_type == FG_GC && > >>> sbi->next_victim_seg[FG_GC] != NULL_SEGNO) { > >>> p.min_segno = sbi->next_victim_seg[FG_GC]; > >>> *result = p.min_segno; > >>> sbi->next_victim_seg[FG_GC] = NULL_SEGNO; > >>> - goto got_result; > >>> } > >>> + > >>> + secno = GET_SEC_FROM_SEG(sbi, segno); > >>> + > >>> + if (sec_usage_check(sbi, secno)) > >>> + goto next; > >>> + > >>> + goto got_result; > >>> } > >> > >> But still allocator can assign this segment after sec_usage_check() > >> in race condition, right? > > Since the BG GC using next_victim takes place after the SIT update in > > do_checkpoint, it seems unlikely that a race condition with > sec_usage_check will occur. > > I mean this: > > - gc_thread > - f2fs_gc > - f2fs_get_victim > - sec_usage_check --- segno #1 is not used in any cursegs > - f2fs_allocate_data_block > - new_curseg > - get_new_segment find segno #1 > > - do_garbage_collect > > Thanks, do_checkpoint sec0 free If sec0 is not freed, then segno1 within sec0 cannot be allocated - gc_thread - f2fs_gc - f2fs_get_victim - sec_usage_check --- segno #1 is not used in any cursegs (but sec0 is already used) - f2fs_allocate_data_block - new_curseg - get_new_segment find segno #1 - do_garbage_collect I appreciate your patch, it is under testing. but I'm wondering if there's a risk of a race condition in this situation > > >> > >> IMO, we can clear next_victim_seg[] once section is free in > >> __set_test_and_free()? something like this: > > I will test it according to your suggestion. > > If there are no issues, can I submit it again with the patch? > > Thanks > >> > >> --- > >> fs/f2fs/segment.h | 13 ++++++++++--- > >> 1 file changed, 10 insertions(+), 3 deletions(-) > >> > >> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h index > >> 0465dc00b349..826e37999085 100644 > >> --- a/fs/f2fs/segment.h > >> +++ b/fs/f2fs/segment.h > >> @@ -473,9 +473,16 @@ static inline void __set_test_and_free(struct > >> f2fs_sb_info *sbi, > >> goto skip_free; > >> next = find_next_bit(free_i->free_segmap, > >> start_segno + SEGS_PER_SEC(sbi), start_segno); > >> - if (next >= start_segno + usable_segs) { > >> - if (test_and_clear_bit(secno, free_i->free_secmap)) > >> - free_i->free_sections++; > >> + if ((next >= start_segno + usable_segs) && > >> + test_and_clear_bit(secno, free_i->free_secmap)) { > >> + free_i->free_sections++; > >> + > >> + if (GET_SEC_FROM_SEG(sbi->next_victim_seg[BG_GC]) == > >> + secno) > >> + sbi->next_victim_seg[BG_GC] = NULL_SEGNO; > >> + if (GET_SEC_FROM_SEG(sbi->next_victim_seg[FG_GC]) == > >> + secno) > >> + sbi->next_victim_seg[FG_GC] = NULL_SEGNO; > >> } > >> } > >> skip_free: > >> -- > >> 2.40.1 > >> > >>>> > >>>>> > >>>>> Because the call stack is different, I think that in order to > >>>>> handle everything at once, we need to address it within > >>>>> do_garbage_collect, or otherwise include it on both sides. > >>>>> What do you think? > >>>>> > >>>>> [30146.337471][ T1300] F2FS-fs (dm-54): Inconsistent segment > >>>>> (70961) type [0, 1] in SSA and SIT [30146.346151][ T1300] Call trace: > >>>>> [30146.346152][ T1300] dump_backtrace+0xe8/0x10c [30146.346157][ > >>>>> T1300] show_stack+0x18/0x28 [30146.346158][ T1300] > >>>>> dump_stack_lvl+0x50/0x6c [30146.346161][ T1300] > >>>>> dump_stack+0x18/0x28 [30146.346162][ T1300] > >>>>> f2fs_stop_checkpoint+0x1c/0x3c [30146.346165][ T1300] > >>>>> do_garbage_collect+0x41c/0x271c [30146.346167][ T1300] > >>>>> f2fs_gc+0x27c/0x828 [30146.346168][ T1300] > >>>>> gc_thread_func+0x290/0x88c [30146.346169][ T1300] > >>>>> kthread+0x11c/0x164 [30146.346172][ T1300] > >>>>> ret_from_fork+0x10/0x20 > >>>>> > >>>>> struct curseg_info : 0xffffff803f95e800 { > >>>>> segno : 0x11531 : 70961 > >>>>> } > >>>>> > >>>>> struct f2fs_sb_info : 0xffffff8811d12000 { > >>>>> next_victim_seg[0] : 0x11531 : 70961 } > >>>>> > >>>>>> > >>>>>> https://lore.kernel.org/linux-f2fs-devel/20250325080646.3291947-2 > >>>>>> - > >>>>>> chao@kernel.org > >>>>>> > >>>>>> Thanks, > >>>>>> > >>>>>>> > >>>>>>> Signed-off-by: Yohan Joung > >>>>>>> --- > >>>>>>> fs/f2fs/gc.c | 4 ++++ > >>>>>>> 1 file changed, 4 insertions(+) > >>>>>>> > >>>>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c index > >>>>>>> 2b8f9239bede..4b5d18e395eb 100644 > >>>>>>> --- a/fs/f2fs/gc.c > >>>>>>> +++ b/fs/f2fs/gc.c > >>>>>>> @@ -1926,6 +1926,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, > >>>>>>> struct > >>>>>> f2fs_gc_control *gc_control) > >>>>>>> goto stop; > >>>>>>> } > >>>>>>> > >>>>>>> + if (__is_large_section(sbi) && > >>>>>>> + IS_CURSEC(sbi, GET_SEC_FROM_SEG(sbi, segno))) > >>>>>>> + goto stop; > >>>>>>> + > >>>>>>> seg_freed = do_garbage_collect(sbi, segno, &gc_list, gc_type, > >>>>>>> gc_control->should_migrate_blocks, > >>>>>>> gc_control->one_time); > >>>>> > >>> > >