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From: Shakeel Butt To: Andrii Nakryiko Cc: bpf@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, adobriyan@gmail.com, hannes@cmpxchg.org, ak@linux.intel.com, osandov@osandov.com, song@kernel.org, jannh@google.com, linux-fsdevel@vger.kernel.org, willy@infradead.org, Omar Sandoval Subject: Re: [PATCH v4 bpf-next 06/10] lib/buildid: implement sleepable build_id_parse() API Message-ID: References: <20240807234029.456316-1-andrii@kernel.org> <20240807234029.456316-7-andrii@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240807234029.456316-7-andrii@kernel.org> X-Migadu-Flow: FLOW_OUT X-Stat-Signature: 4uak55xi5u6h9y74fu3egst5ri7xxhd6 X-Rspam-User: X-Rspamd-Queue-Id: EA1501C0038 X-Rspamd-Server: rspam02 X-HE-Tag: 1723142419-767472 X-HE-Meta: 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 w3mQ27H0 Yb1aqdAWVRKyxUbjZDR6QRjGcR2HQYWvXHSnLhK2LB1f8/WUQHKZmRX+VgpvtnREdGmr8T+sCHvEPYGYTBcVQcIh6cPYJ9IQfoK5WyGwpVaKQtfGD1gRMU25cvBGbscJgdQhVlnD49dkEKvdaR+xRrjQyJgrLnbiV3lekMoI1pQVYe1z5gRBT0rasN6y1j9X0NAIXgS1+wwfa+/1nEy00gnGiZcPakLqKgYSAnxR4717AHPSaqC7vA9pvUW/bB9MVdEpwijjtfxFgHUMVvPeizIKtAxqBBlC+7IBXLHOavXHz9nKUDjlIgApoJIKok6NB4n+6WixXP/IT8wRC12pFoZso5Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 07, 2024 at 04:40:25PM GMT, Andrii Nakryiko wrote: > Extend freader with a flag specifying whether it's OK to cause page > fault to fetch file data that is not already physically present in > memory. With this, it's now easy to wait for data if the caller is > running in sleepable (faultable) context. > > We utilize read_cache_folio() to bring the desired folio into page > cache, after which the rest of the logic works just the same at folio level. > > Suggested-by: Omar Sandoval > Cc: Shakeel Butt > Cc: Johannes Weiner > Signed-off-by: Andrii Nakryiko > --- > lib/buildid.c | 44 ++++++++++++++++++++++++++++---------------- > 1 file changed, 28 insertions(+), 16 deletions(-) > > diff --git a/lib/buildid.c b/lib/buildid.c > index 5e6f842f56f0..e1c01b23efd8 100644 > --- a/lib/buildid.c > +++ b/lib/buildid.c > @@ -20,6 +20,7 @@ struct freader { > struct folio *folio; > void *addr; > loff_t folio_off; > + bool may_fault; > }; > struct { > const char *data; > @@ -29,12 +30,13 @@ struct freader { > }; > > static void freader_init_from_file(struct freader *r, void *buf, u32 buf_sz, > - struct address_space *mapping) > + struct address_space *mapping, bool may_fault) > { > memset(r, 0, sizeof(*r)); > r->buf = buf; > r->buf_sz = buf_sz; > r->mapping = mapping; > + r->may_fault = may_fault; > } > > static void freader_init_from_mem(struct freader *r, const char *data, u64 data_sz) > @@ -63,6 +65,11 @@ static int freader_get_folio(struct freader *r, loff_t file_off) > freader_put_folio(r); > > r->folio = filemap_get_folio(r->mapping, file_off >> PAGE_SHIFT); > + > + /* if sleeping is allowed, wait for the page, if necessary */ > + if (r->may_fault && (IS_ERR(r->folio) || !folio_test_uptodate(r->folio))) > + r->folio = read_cache_folio(r->mapping, file_off >> PAGE_SHIFT, NULL, NULL); Willy's network fs comment is bugging me. If we pass NULL for filler, the kernel will going to use fs's read_folio() callback. I have checked read_folio() for fuse and nfs and it seems like for at least these two filesystems the callback is accessing file->private_data. So, if the elf file is on these filesystems, we might see null accesses.