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Sat, 31 Oct 2026 15:33:53 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 7wtQKGEK5mpbEwAAD6G6ig (envelope-from ); Sat, 31 Oct 2026 15:33:53 +0000 Date: Sat, 31 Oct 2026 16:33:53 +0100 Message-ID: <87fqxlsx3y.wl-tiwai@suse.de> From: Takashi Iwai To: Sasha Levin Cc: Takashi Iwai , Jaroslav Kysela , linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ALSA: memalloc: Free the new pages when WC DMA mapping fails In-Reply-To: <20261028144441.992127-1-sashal@kernel.org> References: <20261028144441.992127-1-sashal@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 4BC141F749 X-Spam-Level: X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Flag: NO X-Spamd-Result: default: False [-12.51 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[5]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; DKIM_TRACE(0.00)[suse.de:+] X-Spam-Score: -12.51 On Wed, 28 Oct 2026 15:44:41 +0100, Sasha Levin wrote: > > snd_dma_wc_alloc() keeps the newly allocated pages in a local variable, > and snd_dma_alloc_dir_pages() stores them in dmab->area only after > ->alloc() returns. If dma_map_single() fails, the error path passes > dmab->area to do_free_pages() instead, and that is still NULL at this > point for the usual callers. > > The pages are then leaked with their write-combining attribute still > set, set_memory_wb() warns about the zero address, and for buffers > larger than a page free_pages_exact() goes on to free the struct pages > of the bogus addresses 4096, 8192 and so on. With CONFIG_DEBUG_VM that > hits the VM_BUG_ON() in free_pages(): > > kernel BUG at mm/page_alloc.c:5600! > RIP: 0010:free_pages_exact+0xcb/0xd0 > Call Trace: > snd_dma_wc_alloc+0x14f/0x160 [snd_pcm] > snd_dma_alloc_dir_pages+0x4f/0x80 [snd_pcm] > > This was reproduced on an x86 guest without swiotlb by allocating > SNDRV_DMA_TYPE_DEV_WC buffers for a device with a 24-bit streaming DMA > mask, so that dma_map_single() fails. > > Free the pages that were just allocated. > > Fixes: c880a5146642 ("ALSA: memalloc: Use proper DMA mapping API for x86 WC buffer allocations") > Signed-off-by: Sasha Levin Applied now. Thanks. Takashi