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 17BCD285CAE for ; Fri, 13 Mar 2026 23:46:18 +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=1773445579; cv=none; b=NWDfVg355fMIpNORT9CQWQUbw6fQTzhMXLkOdZKE4AJnauJSCrVUu6BL9A3WLb/J5Gk54a4U7Y8ksObmWVc1LKe9Otm8+/2Mx7JTtbm1JhqjattIJNsVvW5nhaWlnJQJqSZH5E6DSu2PeTH3dIbVLDL/zF0WmVKOniNy4qnva6g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773445579; c=relaxed/simple; bh=1F3fbIVyxe721BfUqOiVZA7awAX/GI9/8eWNpIS3ANU=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=O3x8GxnlBZFG/fvdF/nscViXA++LXjsO0aWimYxqEbCByW+YZoQMYNnQjKf3RIwztRhcrRvvvPdHoDafYc4OYuSp5YkO7n+gIOZFjdvEbjf6I+c6e2iSTJ/zsU1IhadhwenvovnII0ITsxIZTBSZPwKiiMTQGig39lTeGIjRltc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KjnRypMH; 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="KjnRypMH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6558C19421; Fri, 13 Mar 2026 23:46:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773445578; bh=1F3fbIVyxe721BfUqOiVZA7awAX/GI9/8eWNpIS3ANU=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=KjnRypMHHaZm8iROPnbPjSUjaV8tOwGaeVkSp0xTSh31HxJawrVdvtxxDBgEEBjJ/ qZZ8fxGlacdSrnMi7+4ncwGoSZjd8esS/QFe+rPRWZrcL6vtoNEP9aCuTgmsf07WnL FrDnIL+k5tnQNnPj3qpt0V/WUTXlaLbXyF00LKrvWjCWh9o6+c51N+E4MI1wQ9qEj0 yl7eSrib1ywJEQ1wUhmhtvPY8fNtzmUzPpcdhm6DfisqfOA/kc1GZaOnQ/J6cy16uA RpnmaSocJ16QdrNKEUB4avIXKPng2eThDZQBLs4Rex88xKWx+a6mEZu0duK+0ZFfnJ NYRI/0sHEfSAw== Message-ID: Date: Sat, 14 Mar 2026 07:46:14 +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-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com, Daeho Jeong Subject: Re: [f2fs-dev] [PATCH] f2fs: fix to skip empty sections in f2fs_get_victim To: Daeho Jeong References: <20260310175428.1156719-1-daeho43@gmail.com> <615947f2-fe08-4875-87d9-baef36897e81@kernel.org> <2625a3fc-7dc6-4764-877c-ffeeeb42276c@kernel.org> Content-Language: en-US From: Chao Yu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2026/3/14 00:21, Daeho Jeong wrote: > On Thu, Mar 12, 2026 at 11:49 PM Chao Yu wrote: >> >> On 3/12/2026 11:28 PM, Daeho Jeong wrote: >>> On Thu, Mar 12, 2026 at 2:07 AM Chao Yu wrote: >>>> >>>> On 2026/3/12 00:05, Daeho Jeong wrote: >>>>> On Wed, Mar 11, 2026 at 6:44 AM Chao Yu wrote: >>>>>> >>>>>> On 2026/3/11 01:54, Daeho Jeong wrote: >>>>>>> From: Daeho Jeong >>>>>>> >>>>>>> In age-based victim selection (ATGC, AT_SSR, or GC_CB), f2fs_get_victim >>>>>>> can encounter sections with zero valid blocks. This situation often >>>>>>> arises when checkpoint is disabled or due to race conditions between >>>>>>> SIT updates and dirty list management. >>>>>>> >>>>>>> In such cases, f2fs_get_section_mtime() returns INVALID_MTIME, which >>>>>>> subsequently triggers a fatal f2fs_bug_on(sbi, mtime == INVALID_MTIME) >>>>>>> in add_victim_entry() or get_cb_cost(). >>>>>>> >>>>>>> This patch adds a check in f2fs_get_victim's selection loop to skip >>>>>>> sections with no valid blocks. This prevents unnecessary age >>>>>>> calculations for empty sections and avoids the associated kernel panic. >>>>>>> This change also allows removing redundant checks in add_victim_entry(). >>>>>>> >>>>>>> Signed-off-by: Daeho Jeong >>>>>>> --- >>>>>>> fs/f2fs/gc.c | 9 +++------ >>>>>>> 1 file changed, 3 insertions(+), 6 deletions(-) >>>>>>> >>>>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c >>>>>>> index 2e0f67946914..981eac629fe9 100644 >>>>>>> --- a/fs/f2fs/gc.c >>>>>>> +++ b/fs/f2fs/gc.c >>>>>>> @@ -521,12 +521,6 @@ static void add_victim_entry(struct f2fs_sb_info *sbi, >>>>>>> struct sit_info *sit_i = SIT_I(sbi); >>>>>>> unsigned long long mtime = 0; >>>>>>> >>>>>>> - if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) { >>>>>>> - if (p->gc_mode == GC_AT && >>>>>>> - get_valid_blocks(sbi, segno, true) == 0) >>>>>>> - return; >>>>>>> - } >>>>>>> - >>>>>>> mtime = f2fs_get_section_mtime(sbi, segno); >>>>>>> f2fs_bug_on(sbi, mtime == INVALID_MTIME); >>>>>>> >>>>>>> @@ -889,6 +883,9 @@ int f2fs_get_victim(struct f2fs_sb_info *sbi, unsigned int *result, >>>>>>> if (sec_usage_check(sbi, secno)) >>>>>>> goto next; >>>>>>> >>>>>>> + if (!get_valid_blocks(sbi, segno, true)) >>>>>>> + goto next; >>>>>> >>>>>> Well, for f2fs_get_victim(, AT_SSR), once there are no dirty segment, if we >>>>>> don't count free segment as candidates, then, we can not find any valid victim? >>>>> >>>>> Oh, AT_SSR needs to select the free section in this case? >>>> >>>> I think so, for extreme case. >> >> Oh, check the code again, it seems we select victim from dirty bitmap, >> the victim should not be a free one... >> >> But there is some exceptions: >> >> locate_dirty_segment() >> >> if (valid_blocks == 0 && (!is_sbi_flag_set(sbi, SBI_CP_DISABLED) || >> ckpt_valid_blocks == usable_blocks)) { >> __locate_dirty_segment(sbi, segno, PRE); >> __remove_dirty_segment(sbi, segno, DIRTY); >> >> If valid_blocks equals to zero, but if the checkpoint is disabled and also >> ckpt_valid_blocks doesn't equals to usable_blocks. The segment (or section) >> will still be dirty state in dirty bitmap. >> >> We need to handle this correctly in f2fs_get_victim() correctly before calling >> into add_victim_entry() or get_gc_cost()? >> >> >> /* Don't touch checkpointed data */ >> if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) { >> if (p.alloc_mode == LFS) { >> /* >> * LFS is set to find source section during GC. >> * The victim should have no checkpointed data. >> */ >> if (get_ckpt_valid_blocks(sbi, segno, true)) >> goto next; >> } else { >> /* >> * SSR | AT_SSR are set to find target segment >> * for writes which can be full by checkpointed >> * and newly written blocks. >> */ >> if (!f2fs_segment_has_free_slot(sbi, segno)) >> goto next; >> } >> >> if (!get_valid_blocks(sbi, segno, true)) >> goto next; >> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >> Can this be the fix? > > Did you say AT_SSR can use a free segment? If we put this condition > here, AT_SSR will not use a free segment anymore. Sorry, I remember the wrong place we fallback to allocate a free segment, see get_atssr_segment() below, inside get_ssr_segment() we only search dirty segment/section, once it failed, we call new_curseg() to find a free one. 3083 static int get_atssr_segment(struct f2fs_sb_info *sbi, int type, 3084 int target_type, int alloc_mode, 3085 unsigned long long age) 3086 { 3087 struct curseg_info *curseg = CURSEG_I(sbi, type); 3088 int ret = 0; 3089 3090 curseg->seg_type = target_type; 3091 3092 if (get_ssr_segment(sbi, type, alloc_mode, age)) { 3093 struct seg_entry *se = get_seg_entry(sbi, curseg->next_segno); 3094 3095 curseg->seg_type = se->type; 3096 ret = change_curseg(sbi, type); 3097 } else { 3098 /* allocate cold segment by default */ 3099 curseg->seg_type = CURSEG_COLD_DATA; 3100 ret = new_curseg(sbi, type, true); 3101 } 3102 stat_inc_seg_type(sbi, curseg); 3103 return ret; 3104 } IIUC, in f2fs_get_victim(), we should never expect to find a free segment from dirty bitmap, except for the checkpoint disabled case, that's what we need to fix, right? Thanks, > >> >>>> >>>>> I am confused. Why do we need the below logic? >>>>> Looks like WA for the AT_SSR case? >>>>> >>>>> In f2fs_get_section_mtime() >>>>> out: >>>>> if (unlikely(mtime == INVALID_MTIME)) >>>>> mtime -= 1; >>>>> return mtime; >>>> >>>> There are two conditions, in a section: >>>> >>>> a) if there are no valid blocks, it will return INVALID_MTIME. >>>> b) if there are vaild blocks, it tries to return mtime which is calculated, but >>>> if unlucky the calculated mtime is equal to INVALID_MTIME, in order to distinguish >>>> from case a), we will return INVALID_MTIME - 1 instead. >>> >>> If we find a free segment and pass it to f2fs_get_section_mtime() for >>> (!__is_large_section(sbi)) case. >>> What is the expected output of it? (INVALID_MTIME - 1)? >> >> It depends on the status of section that free segment belong to: >> If there is no valid block in the section, it will return INVALID_MTIME, >> otherwise it will return calcuated mtime, or INVALID_MTIME - 1 for >> extreme case that mtime is just unluckily equals to INVALID_MTIME. >> >> Thanks, >> >>> I don't think this is just an unlucky case. Is this expected result? >>> >>>> >>>> Thanks, >>>> >>>>> >>>>> >>>>>> >>>>>> Thanks, >>>>>> >>>>>>> + >>>>>>> /* Don't touch checkpointed data */ >>>>>>> if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) { >>>>>>> if (p.alloc_mode == LFS) { >>>>>> >>>> >>