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Tue, 21 Apr 2026 03:12:52 +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 qwp0DDTr5mmBOQAAD6G6ig (envelope-from ); Tue, 21 Apr 2026 03:12:52 +0000 Date: Tue, 21 Apr 2026 05:12:51 +0200 From: David Sterba To: Mark Harmstone Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] btrfs: fix double-decrement of bytes_may_use in submit_one_async_extent() Message-ID: <20260421031251.GB12792@twin.jikos.cz> Reply-To: dsterba@suse.cz References: <20260416174359.262120-1-mark@harmstone.com> Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260416174359.262120-1-mark@harmstone.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Spam-Score: -4.00 X-Spam-Level: X-Spamd-Result: default: False [-4.00 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; HAS_REPLYTO(0.30)[dsterba@suse.cz]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.cz:replyto]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; REPLYTO_ADDR_EQ_FROM(0.00)[]; REPLYTO_DOM_NEQ_TO_DOM(0.00)[] X-Spam-Flag: NO On Thu, Apr 16, 2026 at 06:43:51PM +0100, Mark Harmstone wrote: > submit_one_async_extent() calls btrfs_reserve_extent(), which decrements > bytes_may_use. If the call btrfs_create_io_em() fails, we jump to > out_free_reserve, which calls extent_clear_unlock_delalloc(). > > Because we're specifying EXTENT_DO_ACCOUNTING, i.e. > EXTENT_CLEAR_META_RESV | EXTENT_CLEAR_DATA_RESV, this decreases > bytes_may_use again. This can lead to problems later on, as an initial > write can fail only for the writeback to silently ENOSPC. > > Fix this by replacing EXTENT_DO_ACCOUNTING with EXTENT_CLEAR_META_RESV. > This parallels a4fe134fc1d8, which is the same fix in cow_one_range(). ^^^^^^^^^^^^ Please for first occurence put the full commit reference, the same one as for the Fixes tag. Fixed in for-next.