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 EA5643D3CE2; Wed, 21 Jan 2026 18:32:49 +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=1769020370; cv=none; b=IlOlN2fO0kbDVhYWnFLHymDUCZl6ncvfbhmsyRj/RcUVqXItriJU7Sbuc080EL6Bm7SmF3ihmQo2e6tpwYcKQNC9nZvKoceIaBiw9/8UiKEejGFxMn7Y9HpSIbzIpBTbayD3e4e5HNMFW6s/wtG3wDSejDd6EvXyRqwlHruqvEs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769020370; c=relaxed/simple; bh=f6eRpgLLWW1Cn9jN/9owv4SPI9pffncNx2X42ZZOQ/E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BqItHFFHo3Pcmt8P8Of8bCUstpqRTytXYrFUfOXpW8dbzhelJz3RJdKUBDHwc9N5mzmWxBLU/DaiYYCs3/XD2af54XubCldO+LQ42mJqKhVUK1FfRzbBqbLNEsDziZdE4TyWNRZlLyEqYGHdp8/jvfdfSzHLG6Q9MjZ0Q7Ao4TQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=YFVuthBA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="YFVuthBA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2A8B6C4CEF1; Wed, 21 Jan 2026 18:32:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1769020369; bh=f6eRpgLLWW1Cn9jN/9owv4SPI9pffncNx2X42ZZOQ/E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YFVuthBAMdG9+kJcFjRcZKocVH7Ml/TMUjJ9zL/owD7z8vmBfLCdrmv9ktgA2hDbF FS0M1u4ltu2eF0Lzh+md+rqu9DPD4pd/n9z1mKTEV58+1Z5Vyd5JDfTRCzfAKjvok9 Iz0HeiOgUFhgULEVgna/MyMkJ/sbckROR19qzK5U= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Guenter Roeck , "Steven Rostedt (Google)" Subject: [PATCH 6.18 104/198] ftrace: Do not over-allocate ftrace memory Date: Wed, 21 Jan 2026 19:15:32 +0100 Message-ID: <20260121181422.296095897@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260121181418.537774329@linuxfoundation.org> References: <20260121181418.537774329@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Guenter Roeck commit be55257fab181b93af38f8c4b1b3cb453a78d742 upstream. The pg_remaining calculation in ftrace_process_locs() assumes that ENTRIES_PER_PAGE multiplied by 2^order equals the actual capacity of the allocated page group. However, ENTRIES_PER_PAGE is PAGE_SIZE / ENTRY_SIZE (integer division). When PAGE_SIZE is not a multiple of ENTRY_SIZE (e.g. 4096 / 24 = 170 with remainder 16), high-order allocations (like 256 pages) have significantly more capacity than 256 * 170. This leads to pg_remaining being underestimated, which in turn makes skip (derived from skipped - pg_remaining) larger than expected, causing the WARN(skip != remaining) to trigger. Extra allocated pages for ftrace: 2 with 654 skipped WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:7295 ftrace_process_locs+0x5bf/0x5e0 A similar problem in ftrace_allocate_records() can result in allocating too many pages. This can trigger the second warning in ftrace_process_locs(). Extra allocated pages for ftrace WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:7276 ftrace_process_locs+0x548/0x580 Use the actual capacity of a page group to determine the number of pages to allocate. Have ftrace_allocate_pages() return the number of allocated pages to avoid having to calculate it. Use the actual page group capacity when validating the number of unused pages due to skipped entries. Drop the definition of ENTRIES_PER_PAGE since it is no longer used. Cc: stable@vger.kernel.org Fixes: 4a3efc6baff93 ("ftrace: Update the mcount_loc check of skipped entries") Link: https://patch.msgid.link/20260113152243.3557219-1-linux@roeck-us.net Signed-off-by: Guenter Roeck Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ftrace.c | 29 +++++++++++++++-------------- 1 file changed, 15 insertions(+), 14 deletions(-) --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -1122,7 +1122,6 @@ struct ftrace_page { }; #define ENTRY_SIZE sizeof(struct dyn_ftrace) -#define ENTRIES_PER_PAGE (PAGE_SIZE / ENTRY_SIZE) static struct ftrace_page *ftrace_pages_start; static struct ftrace_page *ftrace_pages; @@ -3808,7 +3807,8 @@ static int ftrace_update_code(struct mod return 0; } -static int ftrace_allocate_records(struct ftrace_page *pg, int count) +static int ftrace_allocate_records(struct ftrace_page *pg, int count, + unsigned long *num_pages) { int order; int pages; @@ -3818,7 +3818,7 @@ static int ftrace_allocate_records(struc return -EINVAL; /* We want to fill as much as possible, with no empty pages */ - pages = DIV_ROUND_UP(count, ENTRIES_PER_PAGE); + pages = DIV_ROUND_UP(count * ENTRY_SIZE, PAGE_SIZE); order = fls(pages) - 1; again: @@ -3833,6 +3833,7 @@ static int ftrace_allocate_records(struc } ftrace_number_of_pages += 1 << order; + *num_pages += 1 << order; ftrace_number_of_groups++; cnt = (PAGE_SIZE << order) / ENTRY_SIZE; @@ -3861,12 +3862,14 @@ static void ftrace_free_pages(struct ftr } static struct ftrace_page * -ftrace_allocate_pages(unsigned long num_to_init) +ftrace_allocate_pages(unsigned long num_to_init, unsigned long *num_pages) { struct ftrace_page *start_pg; struct ftrace_page *pg; int cnt; + *num_pages = 0; + if (!num_to_init) return NULL; @@ -3880,7 +3883,7 @@ ftrace_allocate_pages(unsigned long num_ * waste as little space as possible. */ for (;;) { - cnt = ftrace_allocate_records(pg, num_to_init); + cnt = ftrace_allocate_records(pg, num_to_init, num_pages); if (cnt < 0) goto free_pages; @@ -7148,8 +7151,6 @@ static int ftrace_process_locs(struct mo if (!count) return 0; - pages = DIV_ROUND_UP(count, ENTRIES_PER_PAGE); - /* * Sorting mcount in vmlinux at build time depend on * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in @@ -7162,7 +7163,7 @@ static int ftrace_process_locs(struct mo test_is_sorted(start, count); } - start_pg = ftrace_allocate_pages(count); + start_pg = ftrace_allocate_pages(count, &pages); if (!start_pg) return -ENOMEM; @@ -7261,27 +7262,27 @@ static int ftrace_process_locs(struct mo /* We should have used all pages unless we skipped some */ if (pg_unuse) { unsigned long pg_remaining, remaining = 0; - unsigned long skip; + long skip; /* Count the number of entries unused and compare it to skipped. */ - pg_remaining = (ENTRIES_PER_PAGE << pg->order) - pg->index; + pg_remaining = (PAGE_SIZE << pg->order) / ENTRY_SIZE - pg->index; if (!WARN(skipped < pg_remaining, "Extra allocated pages for ftrace")) { skip = skipped - pg_remaining; - for (pg = pg_unuse; pg; pg = pg->next) + for (pg = pg_unuse; pg && skip > 0; pg = pg->next) { remaining += 1 << pg->order; + skip -= (PAGE_SIZE << pg->order) / ENTRY_SIZE; + } pages -= remaining; - skip = DIV_ROUND_UP(skip, ENTRIES_PER_PAGE); - /* * Check to see if the number of pages remaining would * just fit the number of entries skipped. */ - WARN(skip != remaining, "Extra allocated pages for ftrace: %lu with %lu skipped", + WARN(pg || skip > 0, "Extra allocated pages for ftrace: %lu with %lu skipped", remaining, skipped); } /* Need to synchronize with ftrace_location_range() */