From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4753626ACC for ; Thu, 27 Mar 2025 13:47:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743083250; cv=none; b=T2n0dhxBn9pTx0sVDTNxXDun6B2dC7G/AY/ktfZYWlbwn1JbJEfXEi/1PP7jCECIIOuc1Uqj4MHGZlS9tX+bYBN9QrFePqf9odo7UjHLZpG5wj7tS6hF/65ADLlixor8T0Bk6Bf5JPmpCr5iU1hw3SMzk7nsJgd2WHNejpVvkPA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743083250; c=relaxed/simple; bh=6QuAf9mZYKT0w3iBFYWyoO0jHuM/PJ89TbwzBkMY+qo=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=mzmBlTXa50KR4s7r14zCE3MQ6vpaGO/zV3fv/8XYW1uZmBr9g3y04tRycAFzby+0a4EoowT0wpoQ2EcD5ehaqlNXMTq+xvMOW6RXAfc4Xd5/wyz5Sh+s6dt32jTkq2xo5EbuNheqTYWqQbl94xuGeIvL1a2DkJD3HGonEJl/Cy8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AP/tNg3X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AP/tNg3X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 46547C4CEDD; Thu, 27 Mar 2025 13:47:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743083249; bh=6QuAf9mZYKT0w3iBFYWyoO0jHuM/PJ89TbwzBkMY+qo=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=AP/tNg3X5zl4xTlp1ODKhTYOsCVRC4BNbutvj+lKdprbFo2n6FTCnCjST2OTR70/1 PNEDq+csk5tBrSoiTJ8eBE4WBQb55NT5t1Wqu6fBwTKwgxnr7yUylaWezuaFwch7Cf fsQMsqFc6wNbHw+RT6jVKQb0M7fs+zZfcHqvU8j/zlyYuv2iBEFqJq1fj+zXoOAAv+ whAOtCFcx1oALaXkFjQDAk0kCof/MjYvQulZMUbxNChXn32jUFJM2zaziopBFUkEdi Fm5OHUgqOQ86QleTPOe+w+VadgODOxzL8Uv73XBUvxaRS3PanbjDVuOSl9ZmZkLEPY UnahLRth10G9A== Message-ID: <60e763d5-dff4-44a1-9e80-48d384335027@kernel.org> Date: Thu, 27 Mar 2025 21:47:35 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: chao@kernel.org, "linux-f2fs-devel@lists.sourceforge.net" , "linux-kernel@vger.kernel.org" , "pilhyun.kim@sk.com" Subject: Re: [External Mail] Re: [External Mail] Re: [PATCH] f2fs: prevent the current section from being selected as a victim during garbage collection To: "yohan.joung@sk.com" , Yohan Joung , "jaegeuk@kernel.org" , "daeho43@gmail.com" References: <20250326141428.280-1-yohan.joung@sk.com> <2d95428375bd4a5592516bb6cefe4592@sk.com> <8d1f6aa914f94f5da1ccd46c75e9031b@sk.com> Content-Language: en-US From: Chao Yu In-Reply-To: <8d1f6aa914f94f5da1ccd46c75e9031b@sk.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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? IMO, we can clear next_victim_seg[] once section is free in __set_test_and_free()? something like this: --- 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); >>> >