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Mon, 28 Apr 2025 15:04:47 +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 mrSBHA+ZD2igAgAAD6G6ig (envelope-from ); Mon, 28 Apr 2025 15:04:47 +0000 Date: Mon, 28 Apr 2025 17:04:46 +0200 From: David Sterba To: Goldwyn Rodrigues Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] btrfs: correct the order of prelim_ref arguments in btrfs__prelim_ref Message-ID: <20250428150446.GD7139@twin.jikos.cz> Reply-To: dsterba@suse.cz References: 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: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Spam-Level: X-Spamd-Result: default: False [-4.00 / 50.00]; BAYES_HAM(-3.00)[100.00%]; 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]; RCPT_COUNT_TWO(0.00)[2]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; REPLYTO_ADDR_EQ_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:replyto,twin.jikos.cz:mid,suse.com:email,imap1.dmz-prg2.suse.org:helo]; RCVD_COUNT_TWO(0.00)[2]; REPLYTO_DOM_NEQ_TO_DOM(0.00)[] X-Spam-Score: -4.00 X-Spam-Flag: NO On Fri, Apr 25, 2025 at 09:25:06AM -0400, Goldwyn Rodrigues wrote: > btrfs_prelim_ref() calls the old and new reference variables in the > incorrect order. This causes a NULL pointer dereference because oldref > is passed as NULL to trace_btrfs_prelim_ref_insert(). > > Note, trace_btrfs_prelim_ref_insert() is being called with newref as > oldref (and oldref as NULL) on purpose in order to print out > the values of newref. > > To reproduce: > echo 1 > /sys/kernel/debug/tracing/events/btrfs/btrfs_prelim_ref_insert/enable > > Perform some writeback operations. > > Backtrace: > BUG: kernel NULL pointer dereference, address: 0000000000000018 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 115949067 P4D 115949067 PUD 11594a067 PMD 0 > Oops: Oops: 0000 [#1] SMP NOPTI > CPU: 1 UID: 0 PID: 1188 Comm: fsstress Not tainted 6.15.0-rc2-tester+ #47 PREEMPT(voluntary) 7ca2cef72d5e9c600f0c7718adb6462de8149622 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-2-gc13ff2cd-prebuilt.qemu.org 04/01/2014 > RIP: 0010:trace_event_raw_event_btrfs__prelim_ref+0x72/0x130 > Code: e8 43 81 9f ff 48 85 c0 74 78 4d 85 e4 0f 84 8f 00 00 00 49 8b 94 24 c0 06 00 00 48 8b 0a 48 89 48 08 48 8b 52 08 48 89 50 10 <49> 8b 55 18 48 89 50 18 49 8b 55 20 48 89 50 20 41 0f b6 55 28 88 > RSP: 0018:ffffce44820077a0 EFLAGS: 00010286 > RAX: ffff8c6b403f9014 RBX: ffff8c6b55825730 RCX: 304994edf9cf506b > RDX: d8b11eb7f0fdb699 RSI: ffff8c6b403f9010 RDI: ffff8c6b403f9010 > RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000010 > R10: 00000000ffffffff R11: 0000000000000000 R12: ffff8c6b4e8fb000 > R13: 0000000000000000 R14: ffffce44820077a8 R15: ffff8c6b4abd1540 > FS: 00007f4dc6813740(0000) GS:ffff8c6c1d378000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000018 CR3: 000000010eb42000 CR4: 0000000000750ef0 > PKRU: 55555554 > Call Trace: > > prelim_ref_insert+0x1c1/0x270 > find_parent_nodes+0x12a6/0x1ee0 > ? __entry_text_end+0x101f06/0x101f09 > ? srso_alias_return_thunk+0x5/0xfbef5 > ? srso_alias_return_thunk+0x5/0xfbef5 > ? srso_alias_return_thunk+0x5/0xfbef5 > ? srso_alias_return_thunk+0x5/0xfbef5 > btrfs_is_data_extent_shared+0x167/0x640 > ? fiemap_process_hole+0xd0/0x2c0 > extent_fiemap+0xa5c/0xbc0 > ? __entry_text_end+0x101f05/0x101f09 > btrfs_fiemap+0x7e/0xd0 > do_vfs_ioctl+0x425/0x9d0 > __x64_sys_ioctl+0x75/0xc0 > > Signed-off-by: Goldwyn Rodrigues Reviewed-by: David Sterba